Stomatal control in tomato with ABA-deficient roots: response of grafted plants to soil drying

The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA-deficient tomato mutants, sitiens and flacca and their near-isogenic wild-type parent. Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens or flacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA. In the second type of experiment, wild-type shoots were grafted onto a split-root system consisting of one wild-type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild-type roots. In the third type of experiment, grafted plants with wild-type shoots and either wild-type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens. These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.     

Growth of tomato and an ABA-deficient mutant (sitiens) under saline conditions

To determine whether ABA accumulation inhibits or promotes shoot growth under stress, an ABA-deficient mutant tomato, sitiens, and its wild-type, the cultivar Rheinlands Rhum, were exposed to moderate salinity stress. Plants were grown at 75 m M NaCl for 2 weeks under conditions of moderate or high relative humidity (70% and 95% RH, respectively). At 70% RH, shoot DW and relative growth rate were reduced more in sitiens than in the cultivar, but the major difference between genotypes was in the degree of injury suffered by older leaves. Most leaves of sitiens died after 2 weeks, but those of the cultivar remained alive. When plants were grown at 95% RH, to maximize the leaf water status of both genotypes, there was no significant effect of salt on shoot DW of either genotype. However, there was still considerable leaf death in sitiens whereas no visible injury appeared in the cultivar. Cl^– accumulated to higher levels in leaf tissues than Na⁺, but to similar concentrations in both genotypes, and so could not explain the injury in the sitiens leaves. The results indicate that ABA maintains rather than inhibits new growth under stress, and has a major effect on preservation of older leaves.     

Scaling sun and shade photosynthetic acclimation of Alocasia macrorrhiza to whole-plant performance – I. Carbon balance and allocation at different daily photon flux densities

We determined the carbon allocation patterns and construction costs of Alocasia macrorrhiza plants grown at different photon flux densities (PFD) as well as the whole-plant carbon gain of these plants at different daily PFDs. Growth at high PFD resulted in thicker leaves with a higher leaf mass per unit area, and increased biomass allocation to petioles and roots, as compared to growth at low PFD. Increased allocation to petioles may have been necessary to support the heavier leaves, whereas increased allocation to roots may have been necessary to supply sufficient water for the higher transpiration rates in high PFD. Root biomass was highly correlated with the daily, whole-plant transpiration rate. Tissue construction costs per unit dry mass were unchanged by acclimation, but, since the mass per unit areas of leaves, roots and petioles all increased, construction costs per unit leaf area were much higher for plants grown at high PFD. On a per unit leaf area basis, daily whole-plant carbon gain measured at high daily PFD was higher in high- than in low-PFD-grown plants. However, on a per unit leaf mass basis, low-PFD-grown plants had a daily carbon gain at least as high as that of high-PFD-grown plants at high daily PFD. At low daily PFD, low-PFD-grown plants maintained an advantage over high-PFD-grown plants in terms of carbon gain because of their larger leaf area ratios. Thus, in terms of carbon gain, low-PFD-grown plants performed better than sun plants at low PFD and as well as high-PFD-grown plants at high PFD, despite their lower photosynthetic capacities per unit area. For high-PFD-grown plants, the higher construction costs per unit leaf area resulted in lower leaf area ratios, which counteracted the advantage of higher photosynthetic rates per unit leaf area.     

Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability

The study characterized the influence of cucumber mosaic virus (CMV) on the growth response of two annual weeds to nitrogen. Plants were grown individually along a N gradient from 4 to 32 mmol l⁻¹ and data were interpreted using growth analysis. Plant biomass increased with N concentration and was significantly higher for healthy than infected plants at the two highest N concentrations. Healthy plants of Portulaca oleracea L. were characterized by lower biomass allocation to leaves and higher biomass allocation to roots than infected plants; no change in biomass allocation was recorded for Stellaria media Vill. Relative growth rate ( rgr ), net assimilation rate ( nar ) and specific leaf area ( sla ) of plants increased with increasing N concentration. Healthy plants of P. oleracea were characterized by a higher rgr and nar and a lower sla than infected plants, whereas healthy S. media had a higher rgr but a similar nar and sla or leaf weight ratio ( lwr ) compared with infected plants. The consequences of these results on the population dynamics of weeds and virus spread are discussed.     

Relative growth rate, biomass allocation pattern and water use efficiency of three wheat cultivars during early ontogeny as dependent on water availability

We have investigated the water use efficiency of whole plants and selected leaves and allocation patterns of three wheat cultivars (Mexipak, Nesser and Katya) to explore how variation in these traits can contribute to the ability to grow in dry environments. The cultivars exhibited considerable differences in biomass allocation and water use efficiency. Cultivars with higher growth rates of roots and higher proportions of biomass in roots (Nesser and Katya) also had higher leaf growth rates, higher proportions of their biomass as leaves and higher leaf area ratios. These same cultivars had lower rates of transpiration per unit leaf area or unit root weight and higher biomass production per unit water use. They also had higher ratios of photosynthesis to transpiration, and lower ratios of intercellular to external CO₂ partial pressure. The latter resulted from large differences in stomatal conductance associated with relatively small differences in rates of photosynthesis. There was little variation between cultivars in response to drought, and differences in allocation pattern and plant water use efficiency between cultivars as found under well-watered conditions persisted under dry conditions. At the end of the non-watered treatment, relative growth rates and transpiration rates decreased to similar values for all cultivars. High ratios of photosynthesis to transpiration, and accordingly high biomass production per unit of transpiration, is regarded as a favourable trait for dry environments, since more efficient use of water postpones the decrease in plant water status.     

Relative growth rate, biomass allocation pattern and water use efficiency of three wheat cultivars during early ontogeny as dependent on water availability

We have investigated the water use efficiency of whole plants and selected leaves and allocation patterns of three wheat cultivars (Mexipak, Nesser and Katya) to explore how variation in these traits can contribute to the ability to grow in dry environments. The cultivars exhibited considerable differences in biomass allocation and water use efficiency. Cultivars with higher growth rates of roots and higher proportions of biomass in roots (Nesser and Katya) also had higher leaf growth rates, higher proportions of their biomass as leaves and higher leaf area ratios. These same cultivars had lower rates of transpiration per unit leaf area or unit root weight and higher biomass production per unit water use. They also had higher ratios of photosynthesis to transpiration, and lower ratios of intercellular to external CO₂ partial pressure. The latter resulted from large differences in stomatal conductance associated with relatively small differences in rates of photosynthesis. There was little variation between cultivars in response to drought, and differences in allocation pattern and plant water use efficiency between cultivars as found under well-watered conditions persisted under dry conditions. At the end of the non-watered treatment, relative growth rates and transpiration rates decreased to similar values for all cultivars. High ratios of photosynthesis to transpiration, and accordingly high biomass production per unit of transpiration, is regarded as a favourable trait for dry environments, since more efficient use of water postpones the decrease in plant water status.     

Growth and water-use efficiency of 10 Triticum aestivum cultivars at different water availability in relation to allocation of biomass

In environments where the amount of water is limiting growth, water-use efficiency (biomass production per unit water use) is an important trait. We studied the relationships of plant growth and water use efficiency with the pattern of biomass allocation, using 10 wheat cultivars, grown at two soil moisture levels in a growth chamber. Allocation pattern and relative growth rate were not correlated, whereas allocation pattern and water use efficiency were. Variation in transpiration per plant resulted from variation in the rate of transpiration per unit leaf area or root weight, rather than from differences in leaf area or root weight per plant. Transpiration per unit leaf area or root weight was lower when the leaf area or root weight per unit plant weight was larger. Also, the efficiency of water use at the plant and leaf levels was higher for plants with a higher leaf area per unit plant weight, and it was not correlated with the plant's growth rate. Differences in water-use efficiency at the leaf level were related to variation in stomatal conductance, rather than in the rate of photosynthesis. A high photosynthetic water-use efficiency was associated with a low efficiency of nitrogen use for photosynthesis.     

Volatile communication between barley plants affects biomass allocation

Patterns of biomass allocation between different plant organs have often been used to explain the response of plants to variations in resource availability. This paper reports how aerial allelopathy (plant-plant communication) affects biomass allocation, that is the trade-off between root, stem and leaves, and also relative growth rate (RGR, increase in biomass per unit biomass per unit of time, mg g-1 d-1) and its components. Based on previous experiments, communication between two barley (Hordeum vulgare L.) cultivars (Alva and Kara) was used for the present study. Kara exposed to volatiles from Alva allocated significantly more biomass to roots compared with Kara exposed to volatiles from Kara or to clean air. There was no significant difference between plants of Kara exposed to volatiles from Kara and those exposed to clean air. Changes in total dry weight (TDW), RGR and unit leaf rate (ULR, increase in biomass per unit time and leaf area, kg m-2 d-1) were not significantly affected by plant-plant communication. However, there was a significant increase in specific leaf area (SLA, leaf area per leaf dry weight, m2 kg-1) in Kara when exposed to volatiles from Alva. The results show that aerial plant-plant communication does not affect total biomass production but does significantly affect biomass allocation in individual plants. There may be differences in the volatile profiles of Kara and Alva that induce increased biomass allocation to roots in the Kara plants exposed to volatiles from Alva.     

Root morphology and water transport of Pistacia lentiscus seedlings under contrasting water supply: A test of the pipe stem theory

Restoration of degraded Mediterranean areas often requires the reintroduction of key-stone woody species but the establishment of seedlings of native species is frequently poor. This is partly due to insufficient knowledge of the ecology of these species at the seedling stage. Fast rooting and efficient water supply under water limiting conditions may be crucial to withstand summer drought and ensure establishment. However, knowledge of the relationship between root morphology and the water transport capacity of Mediterranean woody species in response to drought is still scarce. We evaluated the effect of low water availability on biomass allocation, root morphology and transpiration of a common Mediterranean shrub species, Pistacia lentiscus L. Seedlings of this species were grown in pots filled with soil under glasshouse conditions for 6 months, and irrigated either weekly (W+) or monthly (W?). Low water availability strongly reduced all fractions of biomass, and decreased relative biomass allocation belowground. Average diameter of fine roots colonising the soil was higher in W+ plants, but this resulted in only marginal effects on specific root length. Water limitation did not affect the topology of secondary roots colonising the soil. Surprisingly, the ratio of leaf area to coloniser roots surface area was higher in W? seedlings. Sapwood area was strongly correlated with leaf area, secondary roots cross-sectional area, and surface area of fine roots colonising the soil when all seedlings were pooled. In agreement with the pipe stem theory, the ratio of sapwood area to leaf area was not affected by watering regime. Plant water loss when soils were taken to field capacity was significantly correlated with leaf area, sapwood area, secondary roots cross-section area and coloniser roots surface area. Water loss at high water availability was greatly reduced in W? plants, as leaf area decreased and transpiration rates on a leaf area basis were similar in W+ and W? seedlings. P. lentiscus showed limited capacity to acclimate to low water availability by modifying biomass allocation and root morphology. Thus, parallel to what has been observed aboveground, this species can benefit from periods of high water availability by showing relatively high root growth rates, but may respond poorly to water scarcity.     

Intraspecific variation in the response of Themeda triandra to defoliation: the effect of time of recovery and growth rates on compensatory growth

Summary The response to a single defoliation was studied on three clones of Themeda triandra collected in the short, mid, and tall grassland regions of the Serengeti National Park (Tanzania). These sites represent a gradient of decreasing grazing intensity. Growth, allocation pattern, and several morphometric traits were monitored during an 80-day period. Clipped plants of the short and medium clones fully compensated for the reduction of biomass, while plants of the tall clone showed overcompensation. During the first two weeks after clipping, clipped plants showed lower relative growth rates than unclipped ones, whereas the opposite was observed later on. Clipped plants compensated for the removal of leaf area by producing new leaves with lower specific weights and higher nitrogen content. They also produced more, smaller tillers. Although clipped plants mobilized nonstructural carbohydrates from roots and crowns, this did not account for a significant amount of growth. Relative growth rates of unclipped plants of the short clone were higher. The relative growth rate of the short clone diminished less after clipping, but also exhibited the lowest increase later. The tall clone was the most negatively affected early, but showed the highest compensation later. Compared to the other clones, the short ecotype showed many of the characteristics that defoliation induced in each individual of any clone: higher allocation to leaf area production, higher relative growth rate, higher number but smaller size of tillers, and lower leaf specific weights.     

Abscisic acid deficiency leads to rapid activation of tomato defence responses upon infection with Erwinia chrysanthemi

In addition to the important role of abscisic acid (ABA) in abiotic stress signalling, basal and high ABA levels appear to have a negative effect on disease resistance. Using the ABA-deficient sitiens tomato ( Solanum lycopersicum ) mutant and different application methods of exogenous ABA, we demonstrated the influence of this plant hormone on disease progression of Erwinia chrysanthemi . This necrotrophic plant pathogenic bacterium is responsible for soft rot disease on many plant species, causing maceration symptoms mainly due to the production and secretion of pectinolytic enzymes. On wild-type (WT) tomato cv. Moneymaker E. chrysanthemi leaf inoculation resulted in maceration both within and beyond the infiltrated zone of the leaf, but sitiens showed a very low occurrence of tissue maceration, which never extended the infiltrated zone. A single ABA treatment prior to infection eliminated the effect of pathogen restriction in sitiens , while repeated ABA spraying during plant development rendered both WT and sitiens very susceptible. Quantification of E. chrysanthemi populations inside the leaf did not reveal differences in bacterial growth between sitiens and WT. Sitiens was not more resistant to pectinolytic cell-wall degradation, but upon infection it showed a faster and stronger activation of defence responses than WT, such as hydrogen peroxide accumulation, peroxidase activation and cell-wall fortifications. Moreover, the rapid activation of sitiens peroxidases was also observed after application of bacteria-free culture filtrate containing E. chrysanthemi cell-wall-degrading enzymes and was absent during infection with an out E. chrysanthemi mutant impaired in secretion of these extracellular enzymes.     

Evidence that abscisic acid does not regulate a centralized whole-plant response to low soil-resource availability

It has been suggested that abscisic acid (ABA) regulates a centralized response of plants to low soil resource availability that is characterized by decreased shoot growth relative to root growth, decreased photosynthesis and stomatal conductance, and decreased plant growth rate. The hypothesis was tested that an ABA-deficient mutant of tomato (flacca; flc) would not exhibit the same pattern of down-regulation of photosynthesis, conductance, leaf area and growth, as well as increased root/shoot partitioning, as its near isogenic wild-type in response to nitrogen or water deficiency, or at least not exhibit these responses to the same degree. Plants were grown from seed in acid-washed sand and exposed to control, nutrient stress, or water stress treatments. Additionally, exogenous ABA was sprayed onto the leaves of a separate group of flc individuals in each treatment. Growth analysis, based on data from frequent harvests of a few individuals, was used to assess the growth and partitioning responses of plants, and gas exchange characteristics were measured on plants throughout the experiment to examine the response of photosynthesis and stomatal conductance. Differences in growth, partitioning and gas exchange variables were found between flc and wild-type individuals, and both nutrient and water treatments caused significant reductions in relative growth rate (RGR) and changes in biomass partitioning. Only the nutrient treatment caused significant reductions in photosynthetic rates. However, flc and wild-type plants responded identically to nutrient and water stress for all but one of the variables measured. The exception was that flc showed a greater decrease in the relative change in leaf area per unit increase of plant biomass (an estimate of the dynamics of leaf area ratio) in response to nutrient stress—a result that is opposite to that predicted by the centralized stress response model. Furthermore, addition of exogenous ABA to flc did not significantly alter any of the responses to nutrient and water stress that we examined. Although it was clear that ABA regulated short-term stomatal responses, we found no evidence to support a pivotal role for ABA, at least absolute amounts of ABA, in regulating a centralized whole-plant response to low soil resource availability.     

Variability in amount and frequency of water supply affects roots but not growth of arid shrubs

Rainfall and soil moisture variability have a strong effect on plant survival and seed germination in arid environments, yet very little is known about the effects on roots and growth of woody seedlings. Here we focused on the effects of variability in both amount and frequency of water supply on juvenile root and leaf functional traits and growth of seven Mediterranean shrub species occurring in arid SE Spain, Anthyllis cytisoides, Atriplex halimus, Ephedra fragilis, Genista umbellata, Lycium intricatum, Retama sphaerocarpa, and Salsola oppositifolia. In a 14-month greenhouse experiment we manipulated water supply expecting that reduced water amount and pulses of watering of different magnitude affected functional traits and seedling growth, even if the amount of water provided was the same. Different watering patterns altered soil drying dynamics, with reduced supply of water amount and frequent watering becoming the driest treatment. We found that roots of all species responded to alterations in water supply by changing biomass allocation patterns (i.e., higher root-to-shoot mass [R:S] ratio in droughted plants), and by altering fine roots diameter, measured in terms of specific root length. Indeed, differences in growth rate among species were significantly linked to fine roots diameter and biomass allocation, which relates to uptake capacity of roots. However, relative growth rate and leaf traits such as specific leaf area were insensitive, likely because prolonged droughts over longer periods of time seem necessary to constraint growth in all these arid shrubs.     

Shoot‐derived abscisic acid promotes root growth

The phytohormone abscisic acid (ABA) plays a major role in regulating root growth. Most work to date has investigated the influence of root‐sourced ABA on root growth during water stress. Here, we tested whether foliage‐derived ABA could be transported to the roots, and whether this foliage‐derived ABA had an influence on root growth under well‐watered conditions. Using both application studies of deuterium‐labelled ABA and reciprocal grafting between wild‐type and ABA‐biosynthetic mutant plants, we show that both ABA levels in the roots and root growth in representative angiosperms are controlled by ABA synthesized in the leaves rather than sourced from the roots. Foliage‐derived ABA was found to promote root growth relative to shoot growth but to inhibit the development of lateral roots. Increased root auxin (IAA) levels in plants with ABA‐deficient scions suggest that foliage‐derived ABA inhibits root growth through the root growth‐inhibitor IAA. These results highlight the physiological and morphological importance, beyond the control of stomata, of foliage‐derived ABA. The use of foliar ABA as a signal for root growth has important implications for regulating root to shoot growth under normal conditions and suggests that leaf rather than root hydration is the main signal for regulating plant responses to moisture.     

NaCI Reduces Indole-3-Acetic Acid Levels in the Roots of Tomato Plants Independent of Stress-Induced Abscisic Acid

Indole-3-acetic acid (IAA) was measured in leaves and roots of tomato (Lycopersicon esculentum) genotypes subjected to salt stress. An abscisic acid (ABA)-deficient mutant of tomato (sitiens), the genetic parent (Rheinlands Ruhm, RR), and a commercial variety (Large Cherry Red, LCR) of tomato were treated with 50 to 300 mM NaCl in nutrient culture. Both LCR and RR had significantly higher levels of IAA in the roots compared with that in sitiens prior to treatment. The initial levels of IAA in the roots of LCR and RR declined by nearly 75% after exposure to NaCl, whereas those in roots from the sitiens mutant remained unchanged. IAA levels in the leaves of all genotypes remained unchanged or increased slightly in response to NaCl. ABA was highest in leaves from the normal genotypes after exposure to NaCl. ABA levels in the roots of sitiens were similar to the levels in the normal genotypes, whereas levels in the leaves were only 10% of the levels found in normal genotypes regardless of the salt treatment. Treatment of LCR and sitiens with exogenous ABA increased the ABA levels in leaves and roots, but there were no measurable changes in endogenous IAA. Therefore, the reduction in IAA appears to result from an ABA-independent effect of NaCl on IAA metabolism in the roots of stressed plants.     

The modular character of growth in Nicotiana tabacum plants under steady-state nutrition

The impact of different plant growth rates on biomass allocation and growth distribution in tobacco was studied on the whole plant, total leaf area and single leaf level. On the whole plant level, constant relationships were found between the total leaf area and the biomass allocation to leaves and the nonphotosynthetic organs (roots and stem) independent from the overall growth rate and the nutrient addition rate to the plants. On the level of total leaf area, plants grown at lower nutrient supply reached a distinct distribution of leaf area later than those grown at higher nutrient supply, but the normalized distribution of leaf area along the stem at a certain plant size did not differ between plants growing at different nutrient supply and growth rates. On the leaf blade level, growth rates declined, initially linearly, from the leaf base to the leaf tip. Distinct gradients within the side veins were not observed, but the growth rates of the side veins were closely correlated to the adjacent mid-vein segments. These gradients flattened with increasing size of the leaf. The modular character of growth in tobacco is discussed in the context of basic growth analysis and as a framework for physiological, cytological, biochemical, and molecular studies in growing plants.Key words: Nicotiana tabacum, whole plant, total leaf area, leaf growth, growth rate, biomass.      

Morphogenetic Changes Induced by a Low Red: Far-Red Ratio and their Growth Consequences in Water Hyacinth (Eichhornia crassipes)

Plants of water hyacinth (Eichhornia crassipes) were grown undertwo red/far-red ratios (Z) to investigate the effects on morphologyand growth of the light quality component of canopy shade. Experimentswere conducted in diffuse sunlight in the presence or absenceof far-red radiation. Under low Z conditions, fewer new ramets were produced and theirstolons were shorter. The number of leaves per ramet was unchanged,but petiole length and blade area were increased. This changein biomass partitioning resulted in a lower investment in themain resource-acquiring organs (leaf blades and roots). Thelower allocation of biomass to the leaf blades was compensatedfor by a higher net assimilation rate, such that relative growthrate remained unchanged. Key words: Biomass partitioning, Eichhornia crassipes, growth, morphogenesis, red: far-red ratio     

基质养分对寄生植物南方菟丝子生长的影响

群落中各营养级的相互作用在群落结构形成中起了重要作用.以南方菟丝子(Cuscuta australis R.Br.)和三叶鬼针草(Biden pilosa L.)为研究对象,采用完全随机区组实验设计方法,测定并分析基质养分(不施肥与施肥)对寄生植物生长的影响,探讨寄生植物生物量与寄主生长特性、生物量和光源捕获能力的相关性.结果表明,施肥显著增加寄生植物南方菟丝子的吸器数量、缠绕圈数、相对盖度、营养器官生物量、生殖器官生物量和总生物量,但对生殖器官的生物量比无显著影响.施肥显著增加寄主植物的根、茎、叶生物量和总生物量、叶生物量比、比叶面积和叶绿素含量,但显著降低根冠比与根生物量比.南方菟丝子生物量与三叶鬼针草生物量、叶生物量比、比叶面积以及相对叶绿素含量之间均存在显著正相关,与根生物量比和根冠比存在显著负相关.研究结果表明施肥可以提高寄主植物的光资源捕获能力,将更多地生物量分配至叶等光合机构上,从而促进寄主植物(生产者)的生长,并间接促进寄生植物(初级消费者)的生长.     

Water relations and growth of original barley plants and its ABA-deficient mutants at increased air temperature

Data on the effects of air temperature increase by 4°C on leaf growth and water relation parameters in barley (Hordeum vulgare L.) plants in original cv. Steptoe and its ABA-deficient mutant (AZ24) are presented. An increase in temperature firstly resulted in the cessation of leaf elongation in both genotypes; however, later in cv. Steptoe plants, as distinct from mutants, the rate of leaf length increment was completely restored. Before air warming, transpiration was more intense in mutant plants; at increased temperature, transpiration was activated in both genotypes. After growth resumption, the water potential in cv. Steptoe plants somewhat increased as compared with initial level (before warming). In AZ34 leaves, in contrast, the water potential, which was initially below that in cv. Steptoe leaves, reduced after temperature increase. The calculation of total hydraulic conductivity of the plants and osmotic hydraulic conductivity in the roots showed that these parameters increased in cv. Steptoe and were not changed in AZ34 mutants. At temperature increase, the level of ABA was not changed in AZ34 mutants, whereas in Steptoe plants it increased in the roots and decreased in the shoots. It was concluded that a capability of ABA synthesis is required for the control of total hydraulic conductivity under changing environmental conditions.