Stomatal Diffusion Resistance of Snap Beans. I. Influence of Leaf-Water Potential

Concurrent measurements of evaporation, leaf conductance, irradiance, leaf water potential, and osmotic potential of maize (Zea mays L. cv. Pa6O2A) in soil at either high or low soil water potential were compared at several hours on two consecutive days in July. Hourly evaporation, measured on two weighing lysimeters, was similar until 1000 hours Eastern Standard Time, but thereafter evaporation from the maize in the dry soil was always less than that in the wet soil; before noon it was 62 % and by midafternoon, only 35 % of that in the wet soil. The leaf water potential, measured with a pressure chamber, was between -1.2 and -2.5 bars and between -6.8 and -8 bars at sunrise (about 0530 hours Eastern Standard Time) in the plants in the wet and dry soil, respectively, but decreased quickly to between -8 and -13 bars in the plants in the wet soil and to less than -15 bars in the plants in the dry soil by 1100 to 1230 hours Eastern Standard Time. At this time, the leaf conductance of all leaves was less than 0.1 cm sec in the maize in the dry soil, whereas the conductance was 0.3 to 0.4 cm sec-' in the leaves near (15), and previous stress history (10). Also, the development of plant water stress is influenced by aerial environment as well as the soil water status. Thus the development of stress and stomatal behavior in a species at high and low soil water potentials, using the data presented in the previous studies, is not a rigorous comparison since the data at the two soil potentials were obtained on different dates and even in different years.In the present study, the stomatal behavior, plant water stress and E of maize in soil at low and high water potentials have been compared over the same period of time and under the same meteorological conditions on plants at the same stage of development. The direct comparison of stomatal behavior and development of plant water stress of plants in moist and dry soil enabled the role of leaf turgor on stomatal behavior to be assessed and the concurrent measurement of E enabled the role of stomatal conductance on E to be evaluated.

Section: Discussionsupporting

confidence: 66%

Concurrent Comparisons of Stomatal Behavior, Water Status, and Evaporation of Maize in Soil at High or Low Water Potential

Turner¹

1975

“…3). This increase in r, with leaf water stress is similar to that found previously in bean (14). In contrast to healthy leaves.…”

Section: Water Relations Of Rust-infected Beanssupporting

confidence: 76%

“…Stomatal closure in response to leaf water stress is responsible for the increase in ri with the decrease in the water content of healthy leaves (14). This closure helps to maintain a balance between the rates of water supply and water loss and thus to prevent injurious water loss.…”

Section: Water Relations Of Rust-infected Beansmentioning

confidence: 99%

Detrimental Effect of Rust Infection on the Water Relations of Bean

Duniway

Durbin

1971

“…Consistent with earlier observations on the common bean, adaxial stomata closed at a higher water potential than abaxial nmon bean (pV) stomata (7). The results presented here extend this differential e textfor details response of adaxial and abaxial stomates to the tepary bean.…”

supporting

confidence: 81%

Comparative Water Relations of Phaseolus vulgaris L. and Phaseolus acutifolius Gray

Markhart

1985

ABSTRACILeaf area expansion, dry weight, and water relations of Phaseolus Pulgaris L. and P. acutifolius Gray were compared during a drying cycle in the greenhouse to understand the characteristics which contribute to the superior drought tolerance ofP. acutifolius. Stomates ofP. acutifolius closed at a much higher water potential than those of P. vulgaris, delaying dehydration of leaf tissue. P. acutifolius had a more deeply penetrating root system, which also contributes to its drought tolerance. Root-shoot ratios did not differ between the two species either under well watered or water stressed conditions. Leaf osmotic potential was also similar in the two species, with no apparent osmotic adjustment during water stress. These results indicate that P. acutifolius postpones dehydration and suggest that sensitive stomates and a deeply penetrating root system are characteristics which, if incorporated into cultivated beans, might increase their drought tolerance.Phaseolus vulgaris L., the common bean, provides an important source of protein in many developing countries. However, it is extremely sensitive to drought, and significant yield reductions due to mild drought are common (4,12). A related species, Phaseolus acutifolius Gray, tepary bean, has been reported to produce extremely well with limited moisture (2,3,13,15,20,21 Leaf area during the drying cycle was determined nondestructively by measuring the length and width of the center leaflet of each trifoliolate leaf. Area of the entire leaf was calculated from regression lines determined from at least 50 leaves of each cultivar grown under similar conditions. Adaxial and abaxial leaf diffusive resistances were measured with a diffusion porometer (Delta Instruments) on the center leaflet ofthe youngest fully expanded leaf. For the common bean this was actually the first trifoliolate leaf. Because of the bushy habit of the tepary bean, a fully expanded, fully exposed leaf was selected. In each case, the leaf was immediately covered with a plastic bag, the petiole excised from the stem, and the water potential measured in a Scholander-type (17) pressure bomb (Soil Moisture Equipment). The leaf was then removed from the bomb and transferred to another zip lock plastic bag and stored on ice for measurement of osmotic potential. Preliminary experiments showed that the measurement of the water potential had no effect on subsequent osmotic potential measurements.Leaves for osmotic potential determination were returned to the laboratory and stored at -20°C until measurement. The leaf 2Abbreviations: WHR, white half runner; PPFD, photosynthetic photon flux density; DAP, days after planting.3 Turface is a product