Application of 10 successive daily heat shocks reduced the growth of c
ontrol tobacco (Nicotiana tabacum L. cv. Petit Havana SR1) plants by a
bout 15%; for Phsp 70-ipt transformed plants this is about 48%. The sh
oot diameter of these ipt-transformed plants increased by about 75%. I
n addition, in heat shock treated ipt-plants (IPT-HS) the upper latera
l buds grew out due to a reduction of apical dominance. The older leav
es of IPT-HS plants had a higher chlorophyll content. In spite of the
observed effects due to a higher endogenous cytokinin content in the I
PT-HS plants, no significant changes were observed on the plasma membr
ane fatty acid composition, nor on its fluidity as determined from the
steady-state fluorescence anisotropy of DPH. Only a minor change in t
he plasma membrane free sterol composition was found as evidenced by a
20% decrease in the stigmasterol to sitosterol ratio in IPT-HS, indic
ative for a possible anti-senescence effect of enhanced endogenous cyt
okinins, but without significant effects on the plasma membrane functi
on. (C) 1997 Elsevier Science Ltd. All rights reserved.