Ca. Parera et al., IMPROVING VIGOR IN SHRUNKEN-2 CORN SEEDLINGS, Journal of the American Society for Horticultural Science, 121(6), 1996, pp. 1069-1075
The shrunken-2 (sh2) mutant of maize (Zea mays L.) increases sucrose a
nd reduces starch in developing endosperm, An associated trait is poor
seed and seedling vigor in seeds containing the mutation, The specifi
c effects of sh2 mutant endosperm on embryo and seedling vigor were de
termined by analyzing seeds that contained either concordant wild-type
or nonconcordant combinations of mutant and wild-type embryo and endo
sperm genotypes, The nonconcordant seed types that contained a wild-ty
pe embryo in association with a sh2 mutant endosperm or a sh2 mutant e
mbryo in association with a wild-type endosperm were generated using t
he TB-3La translocation chromosome in which a wild-type Sh2 gene is at
tached to the centromeric portion of a B chromosome, Under stress cond
itions (complex stress vigor test), the seeds with mutant endosperm ha
d lower germination, seedling fresh and dry weight, and index of condu
ctivity than seeds with wild-type endosperm, Mutant endosperm and embr
yos excised from mutant endosperm imbibed more water than wild-type en
dosperm or embryos excised from wild-type endosperm, Because of the hi
gh concentration of osmotic solutes in the mutant endosperm, a rapid w
ater uptake may induce a membrane disorganization. Leachate conductivi
ties of seeds with mutant endosperm were higher than seeds with wild-t
ype endosperm, In addition, a higher sucrose content and a lower raffi
nose to sucrose ratio were measured in the wild-type embryos associate
d with mutant endosperms than in the normal embryos excised from conco
rdant wild-type seeds, These results suggest that a high rate of water
uptake caused by the elevated concentration of osmotic solutes in see
ds with mutant endosperms may affect membrane integrity during imbibit
ion, Alternatively, the lower raffinose to sucrose ratio present in th
e mutant endosperm class might affect stabilization of cell membranes
during seed desiccation, Embryos cultured in media containing 10% star
ch or no carbohydrate produced smaller seedlings than embryos cultured
in 5% or 10% sucrose. Wild-type embryos excised from mutant endosperm
s exhibited lower germination in 0% and 5% sucrose media than embryos
from concordant seed, indicating that reduced water uptake rates assoc
iated with lower external osmotic potential (10% sucrose) can improve
vigor of embryos associated with sh2 mutant endosperm, The reduced vig
or of embryos and seedlings that develop in association with sh2 mutan
t endosperm can be traced to the physiological and biochemical effects
of the elevated sucrose levels present during seed formation and imbi
bition.