Changes in Photosynthetic Parameters of Evolutionary Different Species of Triticum and Aegilops Grown at High and Low Nitrogen Availability

Abstract

Modern highly productive cultivars of hexaploid crop wheat (Triticum aestivum) developed from wild diploid and tetraploid wheat species and from two species of the genus Aegilops. Several attempts have been undertaken recently to explain the physiological background of differences in growth rate and yield among species representing certain stages of the evolution of crop wheat. It was soon recognized, that no simple relation could be defined between productivity and specific rate of net photosynthetic CO2 uptake (P) by leaves. Evans and Dunstone (1) reported surprising finding that maximum P in flag leaves of modern wheat cultivars is lower than in the wild progenitors. As found in some other studies, the decrease is usually connected with lower nitrogen content in leaves (2), lower rate of Hill reaction (3), and lower content of chlorophyll per leaf mass unit (4). However, the amount of Rubisco was not different among genotypes with different ploidity and its specific activity was found to be higher in hexaploid species (5). It was shown in several other experiments that the potential rate of electron transport reached highest value in tetraploid species (4), and that P may be in some cases considerably higher in hexaploid cultivars than in primitive diploid species. The contrasting results found in the literature could be caused, to some extent, by different cultivation conditions, including variation in nutrient supply. To test this hypothesis we have done our experiments at two levels of mineral nitrogen in substrate.