Krishna S. Nemali

The physiological basis for genetic variation in water use efficiency and carbon isotope composition in Arabidopsis thaliana

Ecologists and physiologists have documented extensive variation in water use efficiency (WUE) in Arabidopsis thaliana, as well as association of WUE with climatic variation. Here, we demonstrate correlations of whole-plant transpiration efficiency and carbon isotope composition (δ13C) among life history classes of A. thaliana. We also use a whole-plant cuvette to examine patterns of co-variation in component traits of WUE and δ13C. We find that stomatal conductance (gs) explains more variation in WUE than does A. Overall, there was a strong genetic correlation between A and gs, consistent with selection acting on the ratio of these traits. At a more detailed level, genetic variation in A was due to underlying variation in both maximal rate of carboxylation (Vcmax) and maximum electron transport rate (Jmax). We also found strong effects of leaf anatomy, where lines with lower WUE had higher leaf water content (LWC) and specific leaf area (SLA), suggesting a role for mesophyll conductance (gm) in variation of WUE. We hypothesize that this is due to an effect through gm, and test this hypothesis using the abi4 mutant. We show that mutants of ABI4 have higher SLA, LWC, and gm than wild-type, consistent with variation in leaf anatomy causing variation in gm and δ13C. These functional data also add further support to the central, integrative role of ABI4 in simultaneously altering ABA sensitivity, sugar signaling, and CO2 assimilation. Together our results highlight the need for a more holistic approach in functional studies, both for more accurate annotation of gene function and to understand co-limitations to plant growth and productivity.

Fertilizer Concentration and Irrigation Method Affect Growth and Fruiting of Ornamental Pepper

Abstract To evaluate the effects of fertilizer concentration and irrigation method on growth of ornamental pepper (Capsicum annuum L. “Treasures Red”), a water-soluble fertilizer solution containing 0, 100, 200, 300, or 400 mg L−1 nitrogen (N) was applied, using subirrigation and hand-watering. Fertilizer concentrations of 200–400 mg L−1 N resulted in an electrical conductivity (EC) gradient from the bottom (lowest EC) to the top (highest EC) of the growing medium in subirrigated, but not in hand-watered pots. The EC in the bottom layer of the medium was affected by irrigation method only at a fertilizer concentration of 400 mg L−1 N. The pH of the growing medium decreased with increasing fertilizer concentration. Shoot dry mass was highest at 200 mg L−1 N in both irrigation treatments and was consistently higher with hand-watering than with subirrigation. Leaf area also was highest at 200 mg L−1 N, but was not affected by irrigation method. In contrast, plant height was greater with subirrigation than with hand-watering, and also peaked at 200 mg L−1 N. Hand-watering increased stem diameter compared to subirrigation and was maximal with 200–400 mg L−1 N. Chlorophyll content of the leaves was much lower at 0 than at 100–400 mg L−1 N, and not affected by irrigation method. Fruit fresh mass was higher with hand-watering than with subirrigation, but shoot dry mass was not affected by irrigation method. Fruiting was poor at 0 mg L−1 N, but did not vary much among fertilizer concentrations ranging from 100–400 mg L−1 N. Subirrigation resulted in earlier flowering and fruit ripening than hand-watering, suggesting that the production period may be a few days shorter with subirrigation. Although N, iron (Fe), and molybdenum (Mo) all increased with increasing fertilizer concentrations, N most likely limited growth at low fertilizer concentrations. In contrast to previous research, these results do not indicate that subirrigated plants should be fertilized with lower concentrations than hand-watered plants.

Plant Abiotic Stress: Water

Fresh water is increasingly becoming a scarce resource. Owing to unpredictable rainfall and limited fresh water resources, water stress has become a greater limiting factor affecting crop productivity than it was previously. We reviewed concepts related to (1) plant water uptake and loss; (2) molecular, metabolic, and physiological changes imposed by water stress in crop species; (3) responses that aid in reducing yield loss under water stress; and (4) industry efforts to develop drought-tolerant hybrids and varieties to aid farmers. Future efforts to combat water stress include combining best agronomic practices, superior genetics, and a multitude of biotechnology-derived traits.