Seasonal variations in some physiological responses of maize (Zea mays L.) under glasshouse conditions

Abstract

In view of the changing climatic conditions mainly related to greenhouse effect, this study was focused on determining the responses of two differentially heat tolerant maize varieties to glasshouse condition. The parameters studies included growth, water relations, gas exchange, photosynthetic pigments, oxidative damage and gene expression. Results revealed that prevailing glasshouse conditions played a crucial role in affecting the maize growth across winter and summer seasons. Despite differences in the growing seasons and varieties glasshouse conditions were adverse for the photosynthetic systems in maize. Major yardsticks of sensitivity were loss of chlorophyll and carotenoids in the light reactions, while reductions in the net photosynthesis and stomatal conductance in the glasshouse grown maize. Prevailing glasshouse conditions were greatly effective in hampering the leaf water relation particularly those of winter sown crop. The glasshouse conditions in winter crop produced oxidative stress on the plants, which was explicit from the increased synthesis of H 2 O 2 , MDA and increased permeability to the ion leakage. Greater free proline accumulation in the tolerant variety not only presented itself as a major amino acid accumulated in environmental stress tolerance but also indicated it as a reliable indicator of tolerance to glasshouse condition in maize. With great varietal difference, changes of temperature and relative humidity inside the glasshouse across the seasons were mainly responsible for the observed changes in mineral nutrients. More distinct changes were evident in K, Ca and nitrate nutrition, which were given greater credence in view of their closer association to the seasonal changes in the environmental conditions inside the glasshouse. Maize seedlings showed sensitivity to high temperature stress, which was recorded from morphological (reduction in shoot fresh weight, dry weight of shoot and root and a reduction in fresh-to-dry weight ratio) and gene expression patterns. The molecular studies suggested that the maize sensitivity to high temperature was mainly due to enhanced coexpression of sag and dhn2 and failure to express hsp70 and sgr2 during relatively long term exposure to high temperature.