Productivity of legume crops grown in semi-arid regions of the world is limited by drought. This study was conducted to determine the effect of drought on the physiological and morphological factors associated with productivity of cowpea (Vigna unguiculata (L.) Walp) and bean (Phaseolus vulgaris L.) grown under reduced water levels. Physiological factors measured were photosynthesis, water and osmotic potential, translocation, RGR and dry matter partitioning. Morphological traits of pods and seeds were studied with scanning electron microscope. Water stress reduced seed yield in cowpea and bean plants by decreasing total biomass and photosynthesis. The source leaf, pod and seed water potential of stressed cowpea was lower than water potential of nonstressed plants. Bean water potential and turgor of source leaf, pod walls, and seed were similar for both stressed and nonstressed plants over the reproductive period. No differences in water potential and turgor were observed between pod walls and seed and source leaves of either cowpea or bean plants. In both bean and cowpea, partitioning of the total above ground dry matter was similar for both stressed and nonstressed plants. However, more dry matter accumulated in seeds than in other plant structures. Photosynthetic rates of single leaves from either cowpea or bean were greater for nonstressed than stressed plants. The duration of seed growth of cowpea and bean was not different between stressed and nonstressed plants; however, rate of seed growth at the end of seed filling period was greater in nonstressed plants. Seed RGR of both stressed and nonstressed cowpea and bean plants declined at about the same time photosynthesis of the source leaf declined. LAI and NAR were greatest in nonstressed cowpea and bean plants. Sixty-one percent of ¹⁴C sucrose taken up by the leaves was translocated to the seeds whereas only about 80% ended up in the pod walls. Pod funiculus of stressed bean plants had more scalariform xylem vessels than nonstressed plants.

Growth of most crop plants (glycophytes) is reduced in saline environments. A few plant species (euhalophytes) not only tolerate, but require salt, and grow optimally in salinities between 100 and 200 mM NaCl. The halophyte Salicornia bigelovii Torr. shows optimal growth in 200 mM NaCl and reduced growth in low saline conditions. In spite of years of research, mechanisms that confer salt tolerance to some plants and sensitivity to others are poorly understood. This research was undertaken to obtain physiological information in an attempt to determine why S. bigelovii requires salt to reach maximum growth. Salicornia seedlings were grown in the greenhouse in aerated nutrient solutions with 5, 200 or 600 mM NaCl. Plants grown in 200 mM NaCl showed optimal growth. Fresh and dry weight of the plants were reduced when grown in 5 and 600 mM NaCl. The main differences in plants grown in 5 and 600 mM NaCl had to do with ion accumulation. These differences in ion accumulation suggested that salt tolerance in Salicornia was established by regulation of ion transport. This was confirmed by studying two primary transport systems in plants grown in 5 or 200 mM NaCl. These transport systems are the H⁺-ATPases on the plasma membrane (PM-ATPase) and the tonoplast (V-ATPase). Higher PM-ATPase (55%) activities were observed in 200 mM NaCl grown plants. Increases in growth and in PM-ATPase activity in Salicornia shoots after exposure to salinity were highly correlated. V-ATPase activity was significantly stimulated in vivo and in vitro (26 and 46%) after exposure to 200 mM NaCl, and this stimulation was Na⁺-specific. Increased V-ATPase activity was consistent with an increased Na⁺ accumulation (45%) compared to plants grown in 5 mM NaCl. Na⁺-stimulation of ATPases may confer salt tolerance in Salicornia by providing the driving force for regulation of intracellular Na⁺ levels. The ATPases provide an increased H⁺ electrochemical gradient across membranes that may be used by the Na⁺/H⁺ exchangers on the plasma membrane and tonoplast. In addition, H⁺ transport across the plasma membrane leads to acidification of the apoplast that is required for cell wall extension and growth. These transport systems need to work in concert for optimal growth and salt tolerance.

Amount and activity of the primary carboxylating enzyme of photosynthesis, photosynthetic gas exchange, and leaf anatomical parameters were measured in two strawberry species, RCP37 (Fragaria chiloensis) and 'Midway' (Fragaria x ananassa). Photosynthetic capacity was greater in RCP37, as indicated by a greater CO₂ assimilation rate at ambient CO₂ concentration (350 μmol mol⁻¹), Rubisco amount, carboxylation efficiency, residual conductance, ratio of mesophyll surface area to leaf area, and leaf N content, compared to 'Midway'. The ratio of mesophyll surface area to leaf area, mesophyll layer thickness and palisade layer thickness were significantly different between RCP37 and 'Midway'. The large surface area of palisade cells in RCP37 accounted for the difference in the ratio of mesophyll surface area to leaf area. Results show that RCP37 has higher photosynthetic capacity than 'Midway'. RCP37 might provide promising resources of germplasm for improving photosynthetic rate or yields of cultivated strawberry varieties.

Pinus brutia var. eldarica is often considered to possess photosynthetic characteristics that make it highly tolerant to drought conditions. However, very little is known about it's photosynthetic response to water stress under either laboratory or field imposed drought conditions. The purpose of this study was to utilize laboratory gas-exchange measurements to determine the effects of water stress and recovery from stress on photosynthetic capacity of potted Pinus brutia via. eldarica plants. Analysis of the rate assimilation (A) versus intercellular CO₂ (Cᵢ) data indicates that recovery of carboxylation efficiency (g'm) (i.e. Rubisco activity and amount) does occur after daily re-watering of moderately stressed (ψ₂ ≃ -2.0 MPa) Pinus brutia. However, these same data indicate that irreversible damage to cell membranes results in an inability to re-generate RubP. Although inferences on the effect of stress on A in field grown Pinus brutia is tenuous, these laboratory results indicate that Pinus brutia may not be as drought tolerant as commonly believed.

Digitaria californica is a warm-season grass native to western hemisphere deserts. This study was conducted to measure: (1) seed dormancy, and the effects of (2) wetting and drying on germination, and (3) glumes on water uptake and loss. Dormancy was measured with weekly germination trials for 12 weeks. Complete and naked caryopses were exposed to a 24-h dry period after 12, 24, 36, and 48-h imbibition, and rewetting for 2 weeks. Water uptake and loss patterns were also measured. Germination percentage increased from about 40% initially to 94% after 9 weeks. Germination speed decreased from 5 days to about 2 days over the same period. Drying reduced percent germination of the 36- and 48-h imbibition treatments for complete caryopses, and that of the 24-, 36-, and 48-h imbibition treatments for naked caryopses. Complete caryopses also seemed to imbibe faster. Moisture loss for complete and naked caryopses appeared similar. Short imbibition periods do not induce germination in this species.

A greenhouse pot experiment was conducted to study the amount of selenium accumulation and the effect of selenite on growth of carrots, squash, and sudan grass. Selenium was added to sandy soil as sodium selenite at five rates (0.02, 0.08, 0.32, 1.28, and 5 mgn) in a randomized complete block design including a control, in three replicates. Addition of 5 mg/l selenium reduced the total biomass (in carrots and squash) as much as 97% and as much as 85% in sudan grass. Crops in the control treatment and those exposed to 0.02 mg/l did not accumulate selenium to levels considered toxic to animals and humans. All other treatments resulted in levels of accumulation that could pose hazards when consumed by animals and humans. Based on the interpolated irrigation concentration that caused 50% yield reduction (observed data), sudan grass was the most tolerant crop (4.0 mg/l)while squash plants were the least tolerant (0.9 mg/l) and carrots were intermediate (2.2 mg/l).

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