| Other Abstract | Water shortage often limits the ecological environment and agricultural production
in the arid and semi-arid area. Understanding the ecophysiological basis of high
efficiency of plant water use is very important for developing water-saving agriculture
and constructing ecological civilization. Plant can maintain water balance with variable
hydraulic properties and aquaporins could be involved, which may help to understand
the ecophysiological mechanisms of plant water relations. This dissertation used the
hydroponically grown maize (Zea mays L.), wheat (Triticum spp.) and sweet sorghum
(Sorghum bicolor (L.) Moench) seedlings as experimental materials, and used cell- and
root- pressure probes, high pressure flow meter and quantitive real-time PCR to
measure the responses of cell, single root, root and shoot and whole-plant hydraulics
and aquaporin genes transcription to short-term and long-term water stress induced by
PEG6000 and root excision. The main results are as follows:
(1). The leaf hydraulic conductivity (K leaf ) of Line 478 varied diurnally and
correlated with whole plant hydraulic conductivity. Similar diurnal rhythms of K leaf and
the root hydraulic conductivity (K root ) could be important to maintaining whole plant
water balance. K root significantly correlated with leaf transpiration rate (E). After 2 h of
osmotic stress, the K root of stressed plants significantly declined but K leaf increased; the
transcription of four ZmPIPs was significantly up regulated in leaves, especially for
ZmPIP1;2, and ZmPIP2;5 was down regulated in roots. The up-regulated K leaf and
down-regulated K root may break the water balance; and ZmPIPs genes may get involved
in the hydraulics changes during short-term water stress.
(2). The E and leaf water potential of 478 varied diurnally, but those of Tian4,
which is more drought resistant, were more constant. Line 478 had advantages on leaf
hydraulic architecture, leaf and root morphology, K leaf and K root , which may contribute to the higher E. The K leaf and K root of both Tian4 and 478 varied diurnally. The K root of
both Tian4 and 478 was reduced under osmotic stress, but the K root of Tian4
subsequently recovered. A lower and rapidly reduced leaf water loss and the recovery of
root hydraulics during short-term osmotic stress may account for the ability of
drought-resistant maize to maintain plant water balance.
(3). The transcription levels of ZmPIPs in mature leaves and roots of well watered
Tian and 478 were significantly different. ZmPIP1;5 was highly expressed in 478 but its
mRNA was not detected in Tian4. Within 2 h of water stress induced by PEG, the
transcription levels of ZmPIPs were up-regulated in roots but were down-regulated in
leaves of Tian4, which may be help to increase water uptake and decrease water loss; in
leaves and roots of 478 plants, the transcription levels of ZmPIPs both showed an
temporary increase, which may contribute to the higher leaf water transpiration.
(4). The E, single root (Lp root ) and cell (Lp cell ) hydraulic conductivity of wheat
increased with increasing ploidy, but the V cell was reduced. Osmotic stress significantly
reduced the E, Lp cell , Lp root , and the relative mRNA content of TaPIP1;2 and TaPIP2;5
in wheat. Under well-watered or osmotic stress conditions, Lp root positively correlated
with the E and Lp cell ; the relative mRNA content of TaPIP1;2 and TaPIP2;5
significantly correlated with Lp cell and Lp root , respectively. Lp cell was reduced, but the
Lp cell /Lp root increased with increasing V cell , suggesting that V cell may affect root radical
water transport. Thus, the increased Lp cell
(5). The P n of stressed plants totally recovered three days later while g s were
consistently lower than the controls, getting an improved instantaneous water-use
efficiency (WUE). During prolonged water stress, the total water loss per plant of
stressed plants reduced significantly, while the dry mass of the whole plant did not
change, and leaf dry mass per unit area increased. The total leaf nitrogen, leaf nitrogen
per unit area and leaf nitrogen concentration of stressed plants reduced significantly. But
the photosynthetic nitrogen-use efficiency (PNUE) and dry mass based nitrogen-use
efficiency (NUE) increased significantly. WUE positively correlated with PNUE. Both
improved water- and nitrogen-use efficiencies of sweet sorghum under water stress may
partly explain its physiological acclimation to drought.
and transcription levels of TaPIP1;2 and
TaPIP2;5 in wheat roots provides insight into the mechanisms underlying enhanced root
water uptake during wheat evolution.
Based on the experimental data obtained from maize, wheat and sweet sorghum grown under controlled conditions, some important issues on the mechanism of
whole-plant water balance were concerned in this dissertation. The results can
contribute to understand the biological bases of plant integrative drought-resistance, to
clarify the physiological mechanisms of water-nitrogen-carbon relations, and to improve
the water use efficiency of plant by gene modification.
KEY WORDS: whole-plant water balance; aquaporin; hydraulic conductivity; SPAC;
drought-resistance; chromosome ploidy; water stress |
Edit Comment