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Semidwarfing Genes Concentrate Photosynthetic Machinery and Affect Leaf Gas Exchange of Wheat

USDA-ARS, Crops Research Lab., 1701 Center Avenue, Fort Collins, CO 80526

R. Wells

Agronomy Dep., North Carolina State Univ., Raleigh, NC

^* Corresponding author.

Although a few previous studies have indicated that leaf photosynthesis in semidwarf wheat (Triticum aestivum L.) plants may be greater than in tall plants, most studies have not supported these findings, and reasons behind the putative photosynthetic differences remain unknown. The purpose of this study was to investigate leaf gas exchange and biochemical traits in a semidwarf winter wheat line (SD;Rht_l,Rht₁,Rht₂,Rht₂) and its nearly isogenic tall counterpart (Tall;rht_l,rht₁,rht₂,rht₂) to determine; (i) whether semidwarfing genes affect leaf photosynthetic rates and (ii) the mechanism that might be involved. Plants of both isolines were grown in pots in growth chambers under four combinations of two irradiance regimes (450 and 950 µmol m^-2 s^-1 photosynthetic photon flux density) and two N regimes. Steady-state gas exchange results were reported for measurements conducted on the most recently fully expanded leaves when the mean Haun growth stage for the main stem was 7. Leaf chlorophyll, soluble protein, and RuBisco concentrations were also assayed on representative leaves, and leaf epidermal impressions taken for characterizing epidermal anatomy. Leaf photosynthetic rates on area and dry weight bases and leaf conductances to water vapor were significantly greater in SD leaves over all treatment combinations. Stomatal density was generally greater and bulliform cell size less in the SD leaves. Concentrations of soluble protein, chlorophyll, and RuBisco were also greater for SD leaves. Measurements of leaf gas exchange and C isotope composition suggest that under some environmental conditions, water use efficiency may be greater in tall plant leaves. We conclude that the reduction in leaf cell sizes associated with introduction of semidwarf stature concentrates the leaf photosynthetic machinery, thereby increasing photosynthetic capacity per unit leaf area or leaf weight.

Received for publication February 21, 1989.

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