Cambial Activity in Acacia Tortilis Subsp. Tortilis is Highest During the Hottest and Driest Month

This study, aimed at elucidating cambial activity and wood formation in Acacia tortilis subsp. tortilis growing in the dry region of Al Baha in Saudi Arabia, reveals that the vascular cambium was active for almost the whole year, producing phloem in two flushes (February to March and then June to August), and xylem for about 11 months. The maximum number of cell layers in the cambial zone (10–13) was observed during June at high temperature, high leaf water deficit and lowest relative humidity (52%) and rainfall. A close relationship existed between the emergence of new leaves and the initiation/acceleration of cambial activity and tissue differentiation. The mean and maximum monthly temperature of the site showed positive and highly significant correlations (p < 0.01) with the width of the cambial zone. The mean monthly relative humidity and mean monthly rainfall were negatively but significantly correlated with cambial activity (p < 0.05). Leaf water deficit had a favorable effect on the cambial activity (r = 0.894, p < 0.01). Acacia tortilis subsp. tortilis has thick-walled vessels of medium diameter and frequency, thick-walled fibers occupying a high tissue proportion, high wood density (0.905 g cm-3) and tannin-like deposits in the vestured vessel pits. The apparent drought tolerance of this species is hypothesized to be due to its deep root system, allowing optimal cambial activity during extreme drought and extremely high day temperatures.

Response of Arabica Coffee Cultivated on Andisols on Organic Matter Applications

Andisols are characterized by dominance of amorphous minerals which form strong and stable bonding with organic matter, therefore Andisols always contain high organic matter. For that reason, organic fertilizer is generally not applied on Andisols, because it is assumed that it will not give any positive effect on growth or yield. The experiment was aimed to evaluate response of mature Kartika 1 Arabica coffee variety (seven years old) cultivated on Andisols applied with organic matter derived from cow dung manure. The experiment was carried out at Andungsari Experimental Station located in Bondowoso District, East Java. Elevation of the site was 1,150 m asl., with rainfall type of C (Schmidt & Fergusson). The experiment was arranged according to completely randomized block design with four replications to evaluate effect of ninecombination treatments of application rates at application depths of 50, 100, and 150 cm. The range of organic fertilizers rates were 0 - 13.5 kg/tree/year. The experiment revealed that cow dung manure applications on Arabica coffee cultivated on Andisols significantly increased yield at the average of 33% compared to the untreated crop. No significant effect of the treatment onvariables of leaf water deficit and soil moisture content during dry season and root density. At range of application depths of 50 - 150 cm, the deeper the organic matter applications, the higher the yield will be.Key words: Andisols, Arabica coffee, organic matter, cow dung manure

Physiological function of non-glandular trichomes in red clover (Trifolium pratense L.)

The objective of the trial was to study the physiological function and potential ecological significance of non-glandular trichomes in red clover based on their relation to the leaf transpiration intensity. The transpiration rate, relative water content and water deficit of the leaves were recorded in field-grown, high and slightly pubescent genotypes. According to results, the presence of nonglandular epidermal trichomes on the leaf surface of red clover was a micromorphological trait related to the regulation of leaf transpiration in stressful conditions. Non-glandular trichomes significantly enhanced water retention of the leaf tissue at high leaf water deficit. In the environmental conditions, limiting leaf evaporation, the pubescent genotypes displayed higher levels of transpiration. It can be suggested that the non-glandular trichomes in red clover are morphological structures supporting the function of leaf stoma apparatus. A positive relation between the degree of pubescence and resistance to powdery mildew was established under natural conditions.

Leaf Dehydration Induces Different Content of Phenolics and Ferulic Acid in Drought-Resistant and -Sensitive Genotypes of Spring Triticale

Analyses of the total pool of phenolic compounds and ferulic acid, as a photoprotector of the photosynthetic apparatus, and the activity of L-phenylalanine ammonia-lyase (PAL), as a key enzyme in phenolics synthesis, were carried out. Measurements were performed on drought-resistant (CHD 12, CHD 147) and -sensitive (CHD 220, CHD 247) genotypes of spring triticale during flowering under increasing leaf water deficit. Additionally, the emission of blue and red fluorescence from leaves were estimated.The exclusively in the resistant triticale genotype CHD 247 observed simultaneous increase in the content of ferulic acid and the total pool of phenolic compounds as a response to the leaf water deficit seems to be a promising biochemical indicator for a reliable selection of genotypes most resistant to drought stress. For the other genotypes, an increase in the total pool of phenolic compounds is accompanied by a decrease in the content of ferulic acid. An increase in the emission of red fluorescence, correlated with the high content of phenolic compounds, indicates the possibilities of these substances participating in the mechanisms of adaptation of the photosynthetic apparatus to water deficit in leaf tissues.

Antioxidative protection in wheat varieties under severe recoverable drought at seedling stag

The antioxidative protection in leaves of four winter wheat (<I>Triticum aestivum </I>L.) varieties with different field drought resistance was studied under severe recoverable soil drought at seedling stage by withholding irrigation for 7 days (57–59% leaf water deficit) followed by rewatering. A 3-fold raise in electrolyte leakage and a sharp increase in proline accumulation corresponded to drought severity. Hydrogen peroxide content and catalase (CAT) activity were maintained low under stress. Peroxidase (GPX) activity increased, whereas superoxide dismutase (SOD) activity only slightly changed. The content of ascorbate and low-molecular thiols diminished under severe drought and was restored in recovery. Malondialdehyde level was not changed significantly in drought-treated plants but raised after re-watering. In recovery CAT activity became significantly higher whereas GPX activity diminished. Three isoforms of SOD, one of catalase and three of GPX were revealed. Proline accumulation had a predominant role in drought response. As for varieties, drought sensitivity or tolerance was not necessarily correlated with differences in the antioxidative response at early vegetative stage.

Alternation of wet and dry sides during partial rootzone drying irrigation alters root-to-shoot signalling of abscisic acid

Partial rootzone drying (PRD) is an irrigation technique where water is distributed unevenly to the root system such that part is irrigated while the remainder is allowed to dry the soil. Tomato (Lycopersicon esculentum Mill.) plants were grown with their roots in two soil columns to compare the physiological consequences of alternation of wet and dry columns during PRD irrigation (alternate PRD, PRD-A) with retention of the same wet and dry columns (fixed PRD, PRD-F). When PRD plants received 50% less water than well-watered (WW) plants, xylem ABA concentration ([X-ABA]) increased and stomatal conductance decreased relative to WW plants. Although both sets of PRD plants received the same amount of water, [X-ABA] of PRD-A plants increased up to 2-fold above that of PRD-F plants, which further decreased stomatal conductance. Differences in [X-ABA] were detected within an hour of alternation, but did not persist beyond the photoperiod of alternation. [X-ABA] increased linearly as whole-pot soil water content (θpot) and leaf water potential (Ψleaf) declined, but the difference in [X-ABA] between the two sets of PRD plants was not due to differences in either θpot or Ψleaf. In PRD-F plants, the unwatered part of the root system contributes proportionally less to the transpiration stream as the soil progressively dries (Yao et al. 2001, Plant, Cell & Environment 24, 227–235). In PRD-A plants, we hypothesise that re-watering the dry part of the root system allows these roots to contribute proportionally more to total sap flux, thus liberating a pulse of ABA to the transpiration stream as the root ABA pool accumulated during soil drying is depleted. Since the enhancement of [X-ABA] caused by PRD-A increased as θpot and Ψleaf declined, an optimal frequency of alternation to maximise the cumulative physiological effects of this ABA pulse must consider possible negative impacts of leaf water deficit as soil water status declines.