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.
