Heat caused redn. in membrane protein thiol level and increased accumulation of thiobarbituric acid reactive substances
in 72 h old germinating tissues thereby reducing germination and early growth performances. Calcium chelator (EGTA),
calcium channel blocker (LaCl3) and calmodulin inhibitor (trifluoperazine) aggravated the effects of heating and added
calcium reversed them, implying that protection against heat induced oxidative damage and improvement of germination
in Amaranthus requires calcium and calmodulin. Imposition of heat stress during early germination also causes
accumulation of reactive oxygen species (ROS) like O2 - and H2O2. Calcium treatment significantly reduced the
accumulation of both the toxic ROS, while EGTA, LaCl3 and TFP treatment enhanced the accumulation. Activities of
antioxidative enzymes catalase (CAT), ascorbate peroxidase (AP) and glutathione reductase (GR) and total thiol content
decreased under heat stress in germinating Amaranthus seedlings. Seedlings raised with Ca2+ treatment under heat
stress exhibit higher activities of CAT, GR and AP and total thiol level than the untreated plants. EGTA, LaCl3 & TFP
treatment, on the other hand significantly reduce the activities of all anti-oxidative enzymes and total thiol level. The work
supports the view that Ca2+-signalling pathway plays significant role in limiting heat induced oxidative injury during
recovery phase of post germination event in Amaranthus lividus.