Apple Autotetraploids—Phenotypic Characterisation and Response to Drought Stress

Polyploidization is an important source of variability for plant breeding. Polyploids are often characterised by increased resistance to biotic and abiotic stresses. Since drought and pathogen attack are the main threats to apple cultivation, obtaining new sources of resistance is an important issue for apple breeding. The newly obtained autotetraploid clones of apple cv. ‘Redchief’ showed superior resistance to fire blight. The aim of the presented research was the in-depth phenotypic characterisation of ‘Redchief’ tetraploids and assessment of their response to drought at the physiological and genetic level. The growth of own-rooted five-year-old trees of ‘Redchief’ tetraploids was poor compared with diploids; all growth parameters—the number and length of current season shoots, the total length of current season shoots per tree and the cross-section area of the trunk—were reduced in tetraploid clones. Grafting on M9 rootstock improved the growth characteristics of ‘Redchief’ tetraploids. Compared with diploid plants, the leaves of tetraploids were thicker, with altered shape, higher chlorophyll content, and larger stomata, but the stomatal density decreased. The leaf anatomical structure of tetraploids was changed, the adaxial and abaxial epidermis and both types of mesophyll were significantly thicker than in diploids. Moreover, the pollen grains of tetraploids were larger, but their viability and germination were reduced. Under conditions of limited water supply, the reduction in growth parameters was smaller and the physiological parameters were higher in the ‘Redchief’ tetraploid clone 4x-25 than in diploid plants. The expression of APX gene was higher in tetraploids than in diploids 15 days after drought stress induction. The results suggest the enhanced drought tolerance of the studied ‘Redchief’ autotetraploid clone compared with its diploid counterpart.

Diurnal stomatal apertures and density ratios affect whole-canopy stomatal conductance, water-use efficiency and yield

Key physiological traits of plants, such as transpiration and stomatal conductance, are usually studied under steady-state conditions or modeled using only a few measured data points. Those measurements do not reflect the dynamic behavior of the plant in response to field conditions. To overcome this bottleneck, we used a gravimetric functional phenotyping platform and a reverse-phenotyping method to examine the dynamic whole-plant water regulation responses of tomato introgression lines and compared those responses with several years of yield performance in commercial fields. Ideotype lines had highly plastic stomatal conductance and high abaxial to adaxial stomatal density ratios and the size of their stomatal apertures peaked early in the day under water-deficit conditions. These traits resulted in dynamic daily water-use efficiency, which allowed for the rapid recovery of transpiration when irrigation was resumed after a period of imposed drought. We found that stomatal density, the abaxial to adaxial stomatal density ratio and the time of maximum stomatal apertures are crucial for plant adaptation and productivity under drought stress conditions. Abaxial stomatal density was also found to be strongly correlated with the expression of the stomatal-development genes SPCH and ZEP. This study demonstrates how a reverse functional phenotyping approach based on field yield data, continuous and simultaneous whole plant waterbalance measurements and anatomical examination of individual leaves can help us to understand and identify dynamic and complex yield-related physiological traits.

Ecophysiological response and morphological adjustment of Argania spinosa L. Skeels under contrasting climates: case study of marginal populations

In this paper, we investigated the seasonal physiological performance and morphological adjustment of Argania spinosa growing under contrasting climatic and biogeographic conditions.Two marginal populations were selected in the main distribution area of the species, one at the Northwest and the other one at the South-west. Trees from the North showed a Mediterranean pattern in Photosynthetic performances, exhibiting maximal carbon assimilation during spring and minimum in summer. In contrast, trees from the South showed a different pattern with maximum values recorded in winter and minimum in spring. Photochemical efficiency of PSII results evidenced the absence of damage to PSII in both sites, probably due to an efficient energy dissipation processed by carotenoid pigments. We recorded increased LMA values in the South, which improves drought resistance. Increasing stomatal length and decreasing stomatal density were registered during the drought season in both populations. A. Spinosa is sensitive to changes in the length of drought stress at its Southern limit. The scarcity of rainfall leading to persistent drought has limited the distribution of the species to the banks of dry Wadis and depressions, where it finds some water compensations during summer. In the North, the summer drought severely impacted the species carbon assimilation.

Particulate Matter (PM) Adsorption and Leaf Characteristics of Ornamental Sweet Potato (Ipomoea batatas L.) Cultivars and Two Common Indoor Plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre)

Particulate matter (PM) is a serious threat to human health, climate, and ecosystems. Furthermore, owing to the combined influence of indoor and outdoor particles, indoor PM can pose a greater threat than urban PM. Plants can help to reduce PM pollution by acting as biofilters. Plants with different leaf characteristics have varying capacities to capture PM. However, the PM mitigation effects of plants and their primary factors are unclear. In this study, we investigated the PM adsorption and leaf characteristics of five ornamental sweet potato (Ipomea batatas L.) cultivars and two common indoor plants (Hedera helix L. and Epipremnum aureum Lindl. & Andre) exposed to approximately 300 μg m−3 of fly ash particles to assess the factors influencing PM adsorption on leaves and to understand the effects of PM pollution on the leaf characteristics of plants. We analyzed the correlation between PM adsorption and photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), leaf area (LA), leaf width/length ratio (W/L), stomatal density (SD), and stomatal pore size (SP). A Pearson’s correlation analysis and a principal component analysis (PCA) were used to evaluate the effects of different leaf characteristics on PM adsorption. The analysis indicated that leaf gas exchange factors, such as Pn and Tr, and morphological factors, such as W/L and LA, were the primary parameters influencing PM adsorption in all cultivars and species tested. Pn, Tr, and W/L showed a positive correlation with PM accumulation, whereas LA was negatively correlated.

CRISPR/Cas9 knockout of EPFL10 reduces stomatal density while maintaining photosynthesis and enhancing water conservation in rice

Rice production is of paramount importance for global nutrition and potential yields will be detrimentally affected by climate change. Rice stomatal developmental genetics were explored as a mechanism to improve water use efficiency while maintaining yield under climate stress. Gene-editing of STOMAGEN and its paralog, EPFL10, using CRISPR/Cas9 in rice cv. Nipponbare yielded lines with altered stomatal densities that were functionally characterized. CRISPR/Cas9 mediated knockouts of EPFL10 and STOMAGEN yielded lines with c. 80% and 25% of wild-type stomata, respectively. epfl10 lines with small reductions in stomatal densities are able to conserve water to similar extents as stomagen lines with large stomatal density reductions but do not suffer from any concomitant reductions in stomatal conductance, carbon assimilation, or thermoregulation. The duplicate of STOMAGEN, EPFL10, is a weak positive regulator of stomatal development in rice. epfl10 lines maintained wild-type physiological characteristics while conserving more water. Modest reductions in stomatal densities may be a climate-adaptive approach in rice that can safeguard yield.

Plant Growth and Stomatal Responses of Potato Cultivars under High Temperature Stress

Background: The higher temperatures resulted due to global warming might bring about changed geographical distribution of crops and even in the season. In other words, heat stress is likely to be an eventual challenge for crop production in general and for potatoes in particular. Thus, imparting heat tolerance in potato cultivars is of utmost importance. Methods: The experiment was conducted in pots and the ambient temperature was approximately 33±0.5oC which constitutes heat stress for potato crop. Potato cultivars namely Kufri Ashoka (relatively heat susceptible) and Kufri Surya (relatively heat tolerant), cultivars, were used in this experiment. The observations were made on the fourth leaf from the top of the mother shoot in potted plants which was fully expanded; data collected were subjected to statistical analysis by using analysis of variance under completely randomized design. Result: Data recorded on different morphological and stomatal attributes indicate that there was significant difference between susceptible and tolerant cultivars of potato wherein Kufri Surya showed better shoot/root ratio, stomatal density as well as stomata index as compared to Kufri Ashoka.

Identification of the ploidy level of plants in grape breeding

Полиплоидные формы обращают на себя внимание своими положительными свойствами, одним из которых является увеличение по сравнению с диплоидными сортами размеров хозяйственно ценных органов. Значительное количество работ по полиплоидии растений в последнее время обусловлено развитием аналитических методов, таких как современные способы приготовления цитогенетических препаратов, цифровая микроскопия, проточная цитометрия, ПЦР-анализ. В настоящее время для получения полиплоидных форм растений используют системы культуры ткани. Успех индукции полиплоидии зависит от различных факторов: состава питательной среды, антимитотического агента, типа эксплантов, времени воздействия и концентрации веществ. В программах создания полиплоидных форм растений проводят исследования с использованием прямого подсчета хромосом, проточной цитометрии, ПЦР-анализа, а также косвенных методов изучения морфологических особенностей объектов. Методы изучения структуры эпидермиса листа являются простыми, быстрыми, неразрушающими и не требующими дорогих реагентов или оборудования. В качестве морфологических индикаторов плоидности обычно используют параметры устьиц (частота устьиц, размеры замыкающих клеток и количество хлоропластов в устьицах). Предлагаются простые протоколы прямого и косвенного методов анализа плоидности винограда. Наиболее успешными работами в области изучения плоидности растений можно считать исследования комплексные. Косвенные методы анализа следует использовать для массового скрининга исходной выборки, прямые методы - для точного изучения генома отобранных растений. Изучение морфологических особенностей эпидермиса листьев может быть использовано в селекционных программах создания виноградных полиплоидов. Исследование дает рациональное обоснование дальнейшей работы по анализу цитогенетических и морфологических особенностей полиплоидных растений винограда. Polyploid forms attract attention for their positive properties, one of which is an increase in the size of economically valuable organs compared to diploid varieties. A significant number of works on plant polyploidy in recent years is due to the development of analytical methods, such as modern methods for the preparation of microslides, digital microscopy, flow cytometry, PCR- analysis. Tissue culture systems are currently used to obtain polyploid forms of plants. The success of polyploidy induction depends on various factors, such as composition of the nutrient medium, antimitotic agent, type of explants, time of exposure, and concentration of substances. In programs for creating polyploid forms of plants, the research is carried out using direct chromosome counting, flow cytometry, PCR-analysis, as well as indirect methods for studying morphological characteristics of objects. Methods for study the structure of leaf epidermis are simple, fast, non-destructive and not requiring expensive reagents or equipment. Stomatal parameters (stomatal density, guard cell size, and the number of chloroplasts in stoma) are commonly used as morphological indicators of ploidy. Simple protocols of direct and indirect methods of ploidy analysis for grapes are proposed. Complex research can be considered as the most successful in the field of plant ploidy studies. Indirect methods of analysis should be used for mass screening of the initial sample, direct methods - for precise study of the genome of selected plants. The study of morphological characteristics of leaf epidermis can be used in breeding programs for the creation of grape polyploids. The research provides a rational basis for further work on the analysis of cytogenetic and morphological features of polyploid grape plants.

Leaf Anatomical Adaptation Under Early Drought Stress of Sugarcane Cultivars – KKU-1999-02 and KKU-1999-03

Anatomical adaptation is an important feature that allows plants to mitigate drought stress. A comparative leaf anatomy of two drought-tolerant sugarcane cultivars, KKU-1999-02 and KKU-1999-03, was studied in early drought stress between 30 and 90 days after planting using peeling and freehand sectioning methods. KKU-1999-02 and KKU-1999-03 showed different anatomical adaptation features, such as increase in cuticle thickness, bulliform cell size, vascular bundle, and stomatal density, and decreases in leaf thickness and stomatal size. KKU-1999-02 showed more remarkable anatomical changes than KKU-1999-03. The results provide important information that can be applied in combination with other agronomic traits in sugarcane breeding programs to expand the adaptation devices of tolerant cultivars under preliminary drought stress.

The SPEECHLESS-induced stomatal increase is required for the salt tolerance of oil palm

Oil palm is the most productive oil producing plant. Salt stress leads to growth damage and decrease in yield of oil palm. However, the physiological responses of oil palm to salt stress and their underlying mechanisms are not clear. RNA-Seq for leaf samples from young palms challenged under three levels of salts (100, 250 and 500 mM NaCl) and control for 14 days was conducted. Diverse signalling pathways were involved in responses to different levels of salt stress. All the three levels of salt stress activated EgSPCH expression and induced stomatal density of oil palm, which was contrasting to that in Arabidopsis. Under strong salt stress group, oil palm removed excessive salt via stomata. Overexpression of EgSPCH in Arabidopsis increased the stomatal production but lowered the salt tolerance. These data suggest that in oil palm, salt activates EgSPCH to generate more stomata in response to salt stress. Our results shed a light on the cellular response to salt stress of oil palm and provide new insights into the mechanisms of different salt-induced stomatal development between halophytes and glycophytes.