Some Effects of Temperature and Irradiance on Growth of the First Four Leaves of Wheat, Triticum aestivum

Plants of Heron wheat were grown at 20 and 15 °C and inquantum flux densities of 400 and 200 µmol m^–2 s^–1.At completion of expansion of the first or second leaf, plantswere transferred between temperatures and quantum flux densities.Final size and cell number were measured for each of the firstfour main-stem leaves. Leaf area was affected only slightlyby treatment and effects on leaf length and width were alsosmall. It was concluded that leaf extension rate, which waslower at the lower temperature and in the lower light regime,is inversely related to the duration of leaf expansion. Leafdry wt was higher for plants grown in high light and for plantsgrown at 15 °C; transfer treatments led to readjustmentswhereby dry wts of leaves expanded after transfer resembledthose of leaves on plants kept throughout in the post-transferconditions. Leaf cell number was not affected by treatment but mean drywt per cell was significantly greater in high light, and forthe first two leaves, at 15 °C. There was a major and highlysignificant effect of treatment on the ratio of dry: fresh wtper cell, this being larger for leaves in high light. Transfertreatments between light regimes led to rapid changes in expandingleaves as was found for leaf dry wt. It was concluded that theexpanding grass leaf is much less dependent on older leavesto provide the necessary materials for cell division and expansionthan is the dicotyledon leaf. It is suggested that the increasein cell dry wt in high light is associated with an increasein cell wall material which is under photomorphogenic control. Triticum aestivum, wheat, leaf growth, cell division, cell expansion, cell size