[Show abstract][Hide abstract] ABSTRACT: The effects of low air humidity and low root temperature (LRT) on water uptake, growth and aquaporin gene expression were investigated in rice plants. The daily transpiration of the plants grown at low humidity was 1.5- to 2-fold higher than that at high humidity. LRT at 13°C reduced transpiration, and the extent was larger at lower humidity. LRT also reduced total dry matter production and leaf area expansion, and the extent was again larger at lower humidity. These observations suggest that the suppression of plant growth by LRT is associated with water stress due to decreased water uptake ability of the root. On the other hand, the net assimilation rate was not affected by low humidity and LRT, and water use efficiency was larger for LRT. We found that low humidity induced coordinated up-regulation of many PIP and TIP aquaporin genes in both the leaves and the roots. Expression levels of two root-specific aquaporin genes, OsPIP2;4 and OsPIP2;5, were increased significantly after 6 and 13 d of LRT exposure. Taken together, we discuss the possibility that aquaporins are part of an integrated response of this crop to low air humidity and LRT.
[Show abstract][Hide abstract] ABSTRACT: Chilling is a major constraint in rice production in cool climates. In rice (Oryza saliva L.) plants, both the air temperature and the water (soil) temperature affect various growth processes independently, and low root zone temperature (thus, root temperature) can inhibit rice growth and yield. In this study, we investigated the effect of low root temperature on rice growth in relation to dry matter production and root water uptake. Plants were grown in hydroponic solutions at two temperatures, one equivalent to air temperature and the other 14 degrees C for 15 d starting 11 d after germination. Low temperature of the solution (low root temperature) inhibited dry matter production of rice plants by decreasing leaf area rather than photosynthetic rate. The response of leaf area was affected by changes in plant water status, that is relative water content (RWC) of stem was decreased by low root temperature resulting in reduced leaf area. The decrease in RWC caused by low root temperature was related to that in root hydraulic conductance (K-r). The responses of transpiration (E) and K-r to the low root temperature depended more on root surface area than on changes in hydraulic conductance per unit root surface area (Lp(r)). These results suggest that dry matter production under the low root temperature condition is controlled mainly by quantitative growth parameters such as leaf area and root surface area.
Plant Production Science 01/2011; 14(1):22-29. DOI:10.1626/pps.14.22 · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The role of root temperature T(R) in regulating the water-uptake capability of rice roots and the possible relationship with aquaporins were investigated. The root hydraulic conductivity Lp(r) decreased with decreasing T(R) in a measured temperature range between 10 degrees C and 35 degrees C. A single break point (T(RC) = 15 degrees C) was detected in the Arrhenius plot for steady-state Lp(r). The temperature dependency of Lp(r) represented by activation energy was low (28 kJ mol(-1)) above T(RC), but the value is slightly higher than that for the water viscosity. Addition of an aquaporin inhibitor, HgCl(2), into root medium reduced osmotic exudation by 97% at 25 degrees C, signifying that aquaporins play a major role in regulating water uptake. Below T(RC), Lp(r) declined precipitously with decreasing T(R) (E(a) = 204 kJ mol(-1)). When T(R) is higher than T(RC), the transient time for reaching the steady-state of Lp(r) after the immediate change in T(R) (from 25 degrees C) was estimated as 10 min, while it was prolonged up to 2-3 h when T(R) < T(RC). The Lp(r) was completely recovered to the initial levels when T(R) was returned back to 25 degrees C. Immunoblot analysis using specific antibodies for the major aquaporin members of PIPs and TIPs in rice roots revealed that there were no significant changes in the abundance of aquaporins during 5 h of low temperature treatment. Considering this result and the significant inhibition of water-uptake by the aquaporin inhibitor, we hypothesize that the decrease in Lp(r) when T(R) < T(RC) was regulated by the activity of aquaporins rather than their abundance.
[Show abstract][Hide abstract] ABSTRACT: Root temperature is found to be a very important factor for leaves to alter the response and susceptibility to chilling stress. Severe visible damage was observed in the most active leaves of seedlings of a japonica rice (Oryza sativa cv. Akitakomachi), e.g. the third leaf at the third-leaf stage, after the treatment where only leaves but not roots were chilled (L/H). On the other hand, no visible damage was observed after the treatment where both leaves and roots were chilled simultaneously (L/L). The chilling injury induced by L/H, a novel type of chilling injury, required the light either during or after the chilling in order to develop the visible symptoms such as leaf bleaching and tissue necrosis. Chlorophyll fluorescence parameters measured after various lengths of chilling treatments showed that significant changes were induced before the visible injury. The effective quantum yield and photochemical quenching of PSII dropped dramatically within 24 h in both the presence and absence of a 12 h light period. The maximal quantum yield and non-photochemical quenching of PSII decreased significantly only in the presence of light. On the other hand, L/H chilling did not affect the function of PSI, but caused a significant decrease in the electron availability for PSI. These results suggest that the leaf chilling with high root temperature destroys some component between PSII and PSI without the aid of light, which causes the over-reduction of PSII in the light, and thereby the visible injury is induced only in the light.
[Show abstract][Hide abstract] ABSTRACT: We analyzed the yield characters of field-grown transgenic potato plants (Solanum tuberosum) carrying a maize gene for sucrose-phosphate synthase (SPS), the key enzyme in sucrose synthesis. The SPS activity in the leaves of transgenic plants (line Ag1203) was 2 times that of the control (cv. May Queen). There was no difference in the photosynthetic CO. uptake rates between Ag1203 and May Queen plants, and the leaf starch content of Ag1203 was lower. These observations indicate that the introduction of a foreign SPS gene improved the supply of photosynthate from source (leaves) to sink (tubers). Additionally, leaf senescence of the transgenic potato plants was delayed relative to that of May Queen. The average tuber weight and total yield of Ag1203 plants were at least 20% higher, and the tuber sucrose content, which is related to eating quality, was also higher. Increased translocation of photosynthate and longer period of photosynthetic activity in the leaves may have increased the yield of Ag1203. These results suggest that introduction of the SPS gene improved the yield characters and quality of potato tubers under field conditions.
Plant Production Science 01/2008; 11(1):104-107. DOI:10.1626/pps.11.104 · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Acclimation to light condition is associated with change in water transport system in napiergrass. In this study, the effects of shading on shoot hydraulic resistance and morphology of napiergrass (Pennisetum purpureum Schumach.) were investigated. In the plants under shading (to 30% of full sunlight) for 30 days (S plants), total hydraulic resistance of a shoot (R-shoot) increased from that of full sunlight (control). In the plants grown under shade condition for 24 d followed by full sunlight conditions for 6 d (SF), the R-shoot value was intermediate between that of control and S plants. A similar response to shading was found in total hydraulic resistance of a stem (R-stem), which accounted for more than 60% of R-shoot, but the total hydraulic resistance of the leaves was not significantly affected by shading. Leaf length, leaf area and stem length were larger, but the stem cross-sectional area (SA) was smaller in S and SF plants than in the control plants. SF plants showed similar leaf length, leaf area and stem length to those in S plants, but the SA in SF plants was slightly larger. Normalization of R-stem by SA and stem length decreased the difference among the treatments, indicating the increase of R-shoot and R-stem under shading resulted from the decrease of SA and the increase of stem length.
Plant Production Science 10/2006; 9(4):364-368. DOI:10.1626/pps.9.364 · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In order to elucidate stomatal response to wind, leaf gas exchange and stomatal conductance in an intact leaf of cucumber plants (Cucumis sativus L.) were measured under different conditions of air current and humidity. A leaf gas exchange cuvette was improved for individual measurements on the abaxial and adaxial leaf surfaces and for adjustment of the leaf boundary air current, where leaf boundary layer conductance can be adjusted at a desired value within a range from 0.3mol m^<-2>s^<-1> to 1.0mol m^<-2>s^<-1>. Rates of leaf gas exchange and stomatal conductance were higher on the abaxial surface than on the adaxial surface. Stomatal response to wind was appeared more sensitive on the abaxial surface, while leaf gas exchange and stomatal conductance on the adaxial surface was scarcely affected by wind. Under the humid air condition, increase in leaf boundary layer conductance significantly enhanced stomatal conductance as well as rates of transpiration and photosynthesis on the abaxial surface. On the other hand, under the dry air condition, stomatal conductance was depressed by increase in leaf boundary layer conductance with little effect on transpiration and photosynthesis. These opposite changes in stomatal conductance found under the humid and dry air conditions were proved visually as change in stomatal aperture by the microscopic observation of the abaxial leaf surface. This stomatal response to wind found on the abaxial surface was not related to feedback stomatal response to transpirational water loss and intercellular CO_2 concentration in the leaf. The mechanism of stomatal response to wind was explained on the basis of water balance within the stomatal complex and on the antagonism relationship between turgors in guard and epidermal cells.
[Show abstract][Hide abstract] ABSTRACT: For individual evaluations of gas exchange parameters on adaxial and abaxial leaf surfaces, the Parkinson leaf cuvette (PP Systems. Ltd., UK) was improved by providing individual air paths to the respective upper (adaxial) and lower (abaxial) leaf cuvettes, where air current in each cuvette was also adjustable independently. The performance of the improved cuvette system was examined by using a wetted filter paper and a cucumber leaf. The three different modes of measurement, i.e. the upper cuvette mode, the lower cuvette mode and the both cuvettes mode, were selected successively, and leaf boundary layer conductance on each surface was arbitrarily adjusted in the range of 0.3 mol m^<-2>s^<-1> to 1.0 mol m^<-2>s^<-1>. The heterogeneity between adaxial and abaxial surfaces of the cucumber leaf was found in gas exchange parameters such as stomatal conductance and rates of transpiration and photosynthesis, and further stomatal response to air current was revealed quantitatively by change in stomatal conductance.
[Show abstract][Hide abstract] ABSTRACT: The characteristics of economical water transport in napiergrass were investigated with respect to water transport regulation by the nodal stem and a water storage capacity (WSC), partly compensation for transpiration with water in the plant. Changes in leaf photosynthesis after plant excisions suggested that water transport to the leaves was mainly regulated by the nodal stem in the morning and the stem base regulated instead in the aftenoon. Contrary to Plant transpiration rate (PTr), water absorption rate by roots (SF) increased slowly and leaf water potential (Ψ[leaf] ) decreased in the morning. However, because of SF increase, Ψ[leaf] gradually recovered in the afternoon. It was condired thar water condifions would be related to the contribute to maintenance of PTr, and it was estimated that WSC compensated 8% of total PTr. On the oter hand, WSC of pot-cultivated plant was estimated to be 3% and WSC in stem was higher than that of leaf from the relationship between PTr and decrease in water content of plant parts. It was considered tat these were involved in controlling water balance in napiegrass.
[Show abstract][Hide abstract] ABSTRACT: A pressure flow meter system was newly developed for measuring hydraulic characteristics of plant organs. In the system, the pressurized water flow through plant organs was given at a desired rate by regulating the applied pressure, and hydraulic resistance or conductance of plant organs was determined from the flow rate and the applied pressure at intervals of about 5 minutes. By applying the system, individual evaluations of hydraulic characteristics of node, internode and leaf insertion in a nodal complex were performed on the basis of an analogue circuit of hydraulic resistances, where the hydraulic resistance of the node was divided into halves at the leaf insertion point. From measurements with Epipremnum aureum Bunt., Cucumis sativus L. and Zea mays L., it was indicated that hydraulic conductance of a leaf insertion was significantly lower than those of node and internode. Z. mays with the thickest stem had the highest hydraulic conductance of the internode. On the other hand, the stem-area specific hydraulic conductances of node and internode were the highest in C. sativus with the thinnest stem and the large leaf.