G. Engelen-eigles et al., DNA endoreduplication in maize endosperm cells is reduced by high temperature during the mitotic phase, CROP SCI, 41(4), 2001, pp. 1114-1121
DNA endoreduplication is the replication of nuclear DNA without subsequent
mitosis and cell division, and is believed to be important in maize (Zea ma
ys L.) kernel development. DNA endoreduplication has been shown to be negat
ively affected by high temperature treatments (HTTs) imposed during early k
ernel development in maize; however, the specific period of endosperm devel
opment at which the process is most sensitive to HTT has not been determine
d. To address this issue, HTTs (4 and 6 d at 35 degreesC) were applied to i
n vitro-grown maize kernels starting at 4, 6, 8, 10, or 12 d after pollinat
ion (DAP). Our approach was to isolate endosperms to determine the effect o
f elevated temperature on endosperm fresh weight (FW), number of endosperm
cells, mitotic index, and DNA endoreduplication. The 4- and 6-d HTTs impose
d during the mitotic phase of the endosperm cell cycle (4, 6, and 8 DAP) re
duced nuclei number and kernel FW, delayed cell division, decreased average
DNA content, and reduced the percentage of nuclei in the 24, 48, and 96 C
classes (C is the DNA content of a haploid nucleus in maize). In contrast,
delaying the imposition of the 4- or 6-d HTTs until 10 or 12 DAP (during th
e endoreduplication phase of the endosperm cell cycle) did not affect nucle
i number, average DNA content, and DNA endoreduplication compared to the co
ntrol. Thus, HTTs are most deleterious to DNA endoreduplication, endosperm
FW, and nuclei number when applied during the mitotic phase of the endosper
m cell cycle. These data further show that 4 to 10 DAP is the period during
maize endosperm development that is most sensitive to high temperature, an
d that prolonged exposure restricts entry of mitotic cells into the endored
uplication phase of the cell cycle.