Hw. Koyro et al., ATPASE ACTIVITIES AND MEMBRANE FINE-STRUCTURE OF RHIZODERMAL CELLS FROM SORGHUM AND SPARTINA ROOTS GROWN UNDER MILD SALT STRESS, Botanica acta, 106(2), 1993, pp. 110-119
The study aims at correlations between ultrastructure of rhizodermal m
embranes and ATPase activities of two gramineous C4-species effected b
y salinization of the growth medium. Comparative investigations were d
one with drought-resistant Sorghum and drought-sensitive, salt toleran
t Spartina plants grown under steady-state conditions without or with
40 mol m-3 NaCl. Both species sustained this treatment and showed mark
ed influences of salt on growth but not on root respiration. Generally
, the intramembraneous particle (IMP) frequencies, found on freeze-fra
cture replicates of rhizodermal plasmic fracture faces of the plasmale
mma (P(PF)) and tonoplast (T(PF)), were higher in Sorghum than in Spar
tina. NaCl leads in both species to an increase of the rhizodermal IMP
frequency in the T(PF) (approximately 150 %) and P(PF) (approximately
120 %). The activities of T- and P-ATPase were determined for membran
e vesicles from crude extracts and from isolated protoplasts of roots,
respectively; the results from both preparations were the same. The v
anadate-sensitive tissue ATPase activities increased under salt stress
approximately 5 times in Sorghum and approximately 2 times in Spar-ti
na whilst the nitrate and azide-sensitive tissue ATPase activities inc
reased approximately 6 times only in Sorghum. The combination of the r
esults from the membrane fine structures with the biochemical tests po
ints out that salt-effected increases of ATPase activities of Sorghum
roots were approximately 4 times higher than the increases of IMP freq
uencies on rhizodermal membranes; in Spartina this effect is less inte
nse. It is concluded that a salty environment leads to a higher ATPase
activity per IMP in both species. The stronger reaction of Sorghum is
explainable by the increase in K+/Na+ selectivity of the plasma membr
ane under salt stress. This is not the case for Spartina because the r
oots of this species include salt which subsequently is sequestered by
the salt glands of the leaves.