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Although a few previous studies have indicated that leaf photosynthesis in semidwarf wheat (Triticum aestivumL.) 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;Rhtl,Rht1,Rht2,Rht2) and its nearly isogenic tall counterpart (Tall;rhtl,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‐2s‐1photosynthetic 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.

Many investigations have been conducted during the past few decades to understand the nature of photosynthetic differences among Triticumspp. and related species, yet only limited information on photosynthetic and water use efficiency differences is available among wheat (Triticum aestivumL.) genotypes. The epurpose of this preliminary study was to examine leaf‐gas exchange related leaf traits among winter wheat genotypes in the field to characterize genotypic‐related variation in photosynthesis water‐use efficiency. Fifteen winter wheat genotype, 13 developed in the central and southern Great Plains of the USA and 2 from the USSR, were planted into a Nunn clay loam (fine, montmorillonitic, mesic Aridic Argiustoll) near Fort Follins, CO, in September 1987. Leaf‐gas exchange measurements were performed appoximately weekly on flag leaves of all genotypes from 27 May (early heading stage) through 20 June 1988. Significant genotypic effect were found for photosynthetic rate per leaf area (CER), leaf conductance), (g5leaf water‐use efficiency( WUE8= CER/g5), the ratio of intercellular [CO2]/ambient[CO2], specific leaf weight, and chlorophyll concentration. Among the genotypes with the lowest water use efficiencies were the two old, large‐leaved Soviet genotypes and the two oldest Great Plains genotypes surveyed ‘Vona’ and ‘Sturdy’. Negative associations of leaf size with CER and WUE8were mostly due to differencens in leaf size and CER between the relatively small‐leaved Great Plains genotypes and the large‐leaved Soviet genotype. Significant variation for WUE8among the winter wheat genotypes was due to genotypic‐related differences in both photosynthetic capacity and gs.

Leaf gas exchange theory indicates that carbon isotope discrimination (∆) is negatively associated with CER/g3(leaf CO2exchange rate/conductance). Discovery of genetic variation for ∆ in wheat (Triticum aestivumL.) and other species has generated interest in using carbon isotope discrimination in plant breeding. However, the hypothesized negative association between CER/g3and & has sometimes not been observed in field‐grown crops. In the present study, CER/g3, & of peduncle tissue, plant productivity and yield were examined in eight winter wheat genotypes under both irrigated and nonirrigated field conditions. Water stress‐ and genotype‐induced variations in CER/g3were more consistently correlated with variations in gs than with CER. However, low CER in ‘Bezostaya’ wheat resulted in a consistently low genotypic ranking for CER/g3. In 1988, values of CER/g3increased with water stress, while ∆ values dropped from 18.17 to 17.48‰. These results imply a negative relationship between CER/g3and ∆, consistent with leaf gas exchange theory; however, ∆ was both positively (1988; r= 0.83** [P≤ 0.01]) and negatively (1989; r= ‐0.79* [P≤ 0.05]) associated with CER/g3in irrigated plots. Positive correlations were obtained between ∆ and both biomass productivity (1988, r= 0.54*; 1989, r = 0.45 [P= 0.08]) and grain yield (1988, r= 0.66*; 1989, r = 0.55*) when data were averaged across genotypes and irrigation treatments. Consistently low ∆ values were obtained for ‘Sturdy’, an early‐released, drought‐susceptible cultivar with low productivity. These results suggest that genotypic rankings for peduncle ∆ must be carefully interpreted, as low ∆ can be associated with low yield and stress susceptibility in wheat.

Echinochloa phyllopogonwas grown hydroponically under four root zone gassing treatments to determine aeration effects on the growth and development of the plant root system. Although mesocotyl growth and the number of nodal roots were unaffected by the treatments, other aspects of plant growth were altered. Shoot growth was reduced by hypoxic (5 kPa partial pressure O2in nitrogen gas) and anoxic conditions (O2free nitrogen gas), but not by ethylene (0.1 ppm in air). Seminal root growth was unaffected by hypoxia or ethylene treatments, but was reduced under anoxia. Hypoxic environments stimulated the emergence of roots along the length of the mesocotyl when compared to aerobic controls; anoxic and ethylene treatments had no significant effects. Mesocotyl roots elongated from primordia that were produced de novo in response to the hypoxic treatment. Under hypoxic conditions, aerenchyma was present in the cortex of nodal roots and to a lesser extent in seminal roots, but mesocotyl roots were devoid of aerenchyma under these conditions. The results are compared with the literature concerning flooding and aeration effects on growth and development in other species.