Generative propagation and fertilisation of Stipeae species – wild grasses with ornamental potential

The wild grasses are of increasing interest among landscape architects. The appropriate plant selection is crucial for the subsequent survival and growth of plants in grassy gardens. The aim of the experiment was to assess the influence of seed age (1–3-year old seeds) on the germination of three Stipeae species: Eriocoma occidentalis subsp. californica, Stipa pulcherrima and Hesperostipa curtiseta. The seed weight and germination percentage showed a decline over a period of seed storage. There was 31–84% (depending on species) loss in germinability of 3-year old seeds in comparison to 1-year old seeds. After germination, plants were repotted and treated with Osmocote (a slow-release fertiliser, N15 + P10 + K12). The results indicated that fertilisation significantly increased the number of roots, stems, leaf length, leaf dry weight, chlorophylls and proline content. None of the tested species flowered in the year of sowing but in the next growing season. Plants fertilised in the previous year formed more and of better quality inflorescence stems.

Overexpression Populus d-Type Cyclin Gene PsnCYCD1;1 Influences Cell Division and Produces Curved Leaf in Arabidopsis thaliana

d-type cyclins (CYCDs) are a special class of cyclins and play extremely important roles in plant growth and development. In the plant kingdom, most of the existing studies on CYCDs have been done on herbaceous plants, with few on perennial woody plants. Here, we identified a Populus d-type cyclin gene, PsnCYCD1;1, which is mainly transcribed in leaf buds and stems. The promoter of PsnCYCD1;1 activated GUS gene expression and transgenic Arabidopsis lines were strongly GUS stained in whole seedlings and mature anthers. Moreover, subcellular localization analysis showed the fluorescence signal of PsnCYCD1;1-GFP fusion protein is present in the nucleus. Furthermore, overexpression of the PsnCYCD1;1 gene in Arabidopsis can promote cell division and lead to small cell generation and cytokinin response, resulting in curved leaves and twisted inflorescence stems. Moreover, the transcriptional levels of endogenous genes, such as ASs, KNATs, EXP10, and PHB, were upregulated by PsnCYCD1;1. Together, our results indicated that PsnCYCD1;1 participates in cell division by cytokinin response, providing new information on controlling plant architecture in woody plants.

Intervessel pit membrane thickness best explains variation in embolism resistance amongst stems of Arabidopsis thaliana accessions

Background and Aims The ability to avoid drought-induced embolisms in the xylem is one of the essential traits for plants to survive periods of water shortage. Over the past three decades, hydraulic studies have been focusing on trees, which limits our ability to understand how herbs tolerate drought. Here we investigate the embolism resistance in inflorescence stems of four Arabidopsis thaliana accessions that differ in growth form and drought response. We assess functional traits underlying the variation in embolism resistance amongst the accessions studied using detailed anatomical observations. Methods Vulnerability to xylem embolism was evaluated via vulnerability curves using the centrifuge technique and linked with detailed anatomical observations in stems using light microscopy and transmission electron microscopy. Key Results The data show significant differences in stem P50, varying 2-fold from −1.58 MPa in the Cape Verde Island accession to −3.07 MPa in the woody soc1 ful double mutant. Out of all the anatomical traits measured, intervessel pit membrane thickness (TPM) best explains the differences in P50, as well as P12 and P88. The association between embolism resistance and TPM can be functionally explained by the air-seeding hypothesis. There is no evidence that the correlation between increased woodiness and increased embolism resistance is directly related to functional aspects. However, we found that increased woodiness is strongly linked to other lignification characters, explaining why mechanical stem reinforcement is indirectly related to increased embolism resistance. Conclusions The woodier or more lignified accessions are more resistant to embolism than the herbaceous accessions, confirming the link between increased stem lignification and increased embolism resistance, as also observed in other lineages. Intervessel pit membrane thickness and, to a lesser extent, theoretical vessel implosion resistance and vessel wall thickness are the missing functional links between stem lignification and embolism resistance.

Life cycle of arabidopsis in the international space station - Growth direction of the inflorescence stems in the presence of light under microgravity

ABSTRACTIn the “Space Seed” experiment performed in Kibo module of the International Space Station, growth direction of the inflorescence stem of arabidopsis was examined under space 1 G, μG, and ground 1 G conditions in the presence of light. The stems grew almost upright (vertical to the surface of seedbed) under ground 1 G. Although the stems were primarily upright both under space 1 G and μG, they tilted slightly. The tilting of the stems under space 1 G was indicated to be due to tilting of the artificial gravitational acceleration vectors produced on the centrifuge. The tilting of the stems under μG was suggested to be due to the pressure of directional airflow produced by ventilation.

A novel pathway controlling cambium initiation and - activity via cytokinin biosynthesis in Arabidopsis

Plant secondary growth, also referred to as wood formation, includes the production of secondary xylem, which is derived from meristematic cambium cells embedded in vascular tissues. Despite the importance of secondary xylem in plant growth and wood formation, the molecular mechanism of secondary growth is not yet well understood. Here we identified an important role for the Arabidopsis thaliana (Arabidopsis) AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene, encoding for a putative transcriptional regulator, in controlling vascular cambium activity and secondary xylem formation. Secondary xylem development was significantly reduced in inflorescence stems of the Arabidopsis ahl15 loss-of-function mutant, whereas AHL15 overexpression led to extensive secondary xylem formation. AHL15 expression under a vascular meristem-specific promoter also enhanced the amount of interfascicular secondary xylem. Moreover, AHL15 appeared to be required for the enhanced secondary xylem formation in the Arabidopsis double loss-of-function mutant of the SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and FRUITFULL (FUL) genes. A well-known central regulator of cambial activity is the plant hormone cytokinin. We showed that the expression of two cytokinin biosynthesis genes (ISOPENTENYL TRANSERASE (IPT) 3 and 7) is decreased in ahl15 loss-of-function mutant stems, whereas the secondary xylem deficiency in these mutant stems can be resorted by cambium-specific expression of the Agrobacterium tumefaciens IPT gene, indicating that AHL15 acts through the cytokinin pathway. These findings support a model whereby AHL15 acts as a central factor inducing vascular cambium activity downstream of SOC1 and FUL and upstream of IPT3, IPT7 and LOG4, LOG5 governing the rate of secondary xylem formation in Arabidopsis inflorescence stems.

Living among thorns: herpetofaunal community (Anura and Squamata) associated to the rupicolous bromeliad Encholirium spectabile (Pitcairnioideae) in the Brazilian semi-arid Caatinga

Bromeliads are important habitats for reptiles and amphibians, and are constantly used as shelter, refuge, foraging or thermoregulation sites due to their foliar architecture, which allows for constant maintenance of humidity and temperature. This study aimed to identify the herpetofauna inhabiting the non-phytotelmata rupicolous bromeliad Encholirium spectabile Mart. ex Schult. & Schult.f. and to analyze the microhabitat usage of these bromeliads by different species in the Caatinga of northeastern Brazil. From January 2011 to August 2012, we collected data by active search throughout three paralel transects in a rock outcrop in the municipality of Santa Maria, state of Rio Grande do Norte. We recorded four species of anuran amphibians, six lizards, and seven snakes in the bromeliads. The average air temperature was lower and air humidity higher inside than outside the bromeliads, and bromeliads at the rock outcrop borders had lower temperatures and higher humidity than those at the center. We found a significant difference in the distribution of individuals throughout the rock outcrop, with most specimens found at the borders. We also found significant differences regarding the use of each microhabitat by the taxonomic groups, with lizards and snakes using green leaves and dry leaves evenly, along with fewer records in inflorescence stems, and anurans mainly using green leaves, with few records on dry leaves, and no records in the inflorescence stems. This study highlights rupicolous bromeliads as key elements in the conservation and maintenance of amphibians and reptiles in the rock outcrops of Brazilian semi-arid Caatinga.

The class II KNOX transcription factors KNAT3 and KNAT7 synergistically regulate monolignol biosynthesis in Arabidopsis

The function of the transcription factor KNOTTED ARABIDOPSIS THALIANA7 (KNAT7) is still unclear since it appears to be either a negative or a positive regulator for secondary cell wall deposition with its loss-of-function mutant displaying thicker interfascicular and xylary fiber cell walls but thinner vessel cell walls in inflorescence stems. To explore the exact function of KNAT7, class II KNOTTED1-LIKE HOMEOBOX (KNOX II) genes in Arabidopsis including KNAT3, KNAT4, and KNAT5 were studied together. By chimeric repressor technology, we found that both KNAT3 and KNAT7 repressors exhibited a similar dwarf phenotype. Both KNAT3 and KNAT7 genes were expressed in the inflorescence stems and the knat3 knat7 double mutant exhibited a dwarf phenotype similar to the repressor lines. A stem cross-section of knat3 knat7 displayed an enhanced irregular xylem phenotype as compared with the single mutants, and its cell wall thickness in xylem vessels and interfascicular fibers was significantly reduced. Analysis of cell wall chemical composition revealed that syringyl lignin was significantly decreased while guaiacyl lignin was increased in the knat3 knat7 double mutant. Coincidently, the knat3 knat7 transcriptome showed that most lignin pathway genes were activated, whereas the syringyl lignin-related gene Ferulate 5-Hydroxylase (F5H) was down-regulated. Protein interaction analysis revealed that KNAT3 and KNAT7 can form a heterodimer, and KNAT3, but not KNAT7, can interact with the key secondary cell wall formation transcription factors NST1/2, which suggests that the KNAT3–NST1/2 heterodimer complex regulates F5H to promote syringyl lignin synthesis. These results indicate that KNAT3 and KNAT7 synergistically work together to promote secondary cell wall biosynthesis.

Circumnutation and Growth of Inflorescence Stems of Arabidopsis thaliana in Response to Microgravity under Different Photoperiod Conditions

Circumnutation is a periodic growth movement, which is an important physiological mechanism of plants to adapt to their growth environments. Gravity and photoperiod are two key environmental factors in regulating the circumnutation of plants, but the coordination mechanism between them is still unknown. In this study, the circumnutation of Arabidopsis thaliana inflorescence stems was investigated on board the Chinese recoverable satellite SJ-10 and the Chinese spacelab TG-2. Plants were cultivated in a special plant culture chamber under two photoperiod conditions [a long-day (LD) light: dark cycle of 16:8 h, and a short-day (SD) light: dark cycle of 8:16 h]. The plant growth and movements were followed by two charge-coupled device (CCD) cameras. The parameter revealed a daily (24 h) modulation on both TG-2 and SJ-10, under both the LD and the SD conditions. The inhibition of circumnutation was more apparent by microgravity under the SD in comparison with that under the LD condition, suggesting the synergistic effects of the combined microgravity and photoperiod on the circumnutation in space. In addition, an infradian rhythm (ca. 21 days long) on the TG-2 was also observed.

Effect of planting time and supplemental irradiation on growth and flowering of Lachenalia ‘Romaud’

Growth and flowering of lachenalia ‘Romaud’ was studied with reference to its commercial potential as pot plant and the need to obtain flowering plants at a specific time. The experiment was carried out in a heated glasshouse. Lachenalia bulbs were planted in November, December, January and February. The plants were exposed to two lighting regimes, natural lighting and natural lighting with supplemental irradiation (HPS lamps). The later the planting date was, the faster the bulbs flowered, and they produced thicker inflorescence stems with greater number of florets. Depending on the bulb planting date and light conditions, the plants flowered from February to May. The leaves obtained from the bulbs planted in November and December were longer than those produced by the bulbs planted in January and February. Compared with control, supplemental irradiation accelerated flowering by 10–13 days and positively affected plant features by promoting the growth of thicker inflorescence stems with more abundant and longer florets. The leaves of irradiated bulbs were shorter (apart from the bulbs planted in February) and were characterised by a higher content of chlorophyll a, chlorophyll a + b and carotenoids as compared with control. Plants grown under HPS light also had the higher dry weight of bulbs, leaves and stems.