Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines

Significant genetic variation in leaf photosynthetic rate has been reported in grain sorghum [Sorghum biocolor (L.) Moench]. The relationships between leaf photosynthetic rates and total biomass production and grain yield remain to be established and formed the purpose of this experiment. Twenty two grain sorghum parent lines were tested in the field during the 1988 growing season under well-watered and water-limited conditions. Net carbon assimilation rates were measured at mid-day during the 30 day period from panicle initiation to head exertion on upper-most fully expanded leaves using a portable photosynthesis system (LI-6200). Total biomass and grain production were determined at physiological maturity. The lines exhibited significant genetic variation in leaf photosynthetic rate, total biomass production and grain yield. Significant positive correlations existed between leaf photosynthesis and total biomass and grain production under both well-watered and water-limited conditions. The results suggest that leaf photosynthetic rate measured prior to flowering is a good indicator of productivity in grain sorghum.     

Interactions between Senescence and Leaf Orientation Determine in Situ Patterns of Photosynthesis and Photoinhibition in Field-Grown Rice

Photosynthesis and photoinhibition in field-grown rice (Oryza sativa L.) were examined in relation to leaf age and orientation. Two varieties (IR72 and IR65598-112-2 [BSI206]) were grown in the field in the Philippines during the dry season under highly irrigated, well-fertilized conditions. Flag leaves were examined 60 and 100 d after transplanting. Because of the upright nature of 60-d-old rice leaves, patterns of photosynthesis were determined by solar movements: light falling on the exposed surface in the morning, a low incident angle of irradiance at midday, and light striking the opposite side of the leaf blade in the afternoon. There was an early morning burst of CO₂ assimilation and high levels of saturation of photosystem II electron transfer as incident irradiance reached a maximum level. However, by midday the photochemical efficiency increased again almost to maximum. Leaves that were 100 d old possessed a more horizontal orientation and were found to suffer greater levels of photoinhibition than younger leaves, and this was accompanied by increases in the de-epoxidation state of the xanthophyll cycle. Older leaves had significantly lower chlorophyll content but only slightly diminished photosynthesis capacity.     

中国颚毛虫兆属一新种（弹尾纲：疣虫兆科）

对颚毛虫兆属Crossodonthina Yosii, 1954做了简要介绍,提供了该属的鉴别特征,记述了采自中国湖南省东安县舜皇山的颚毛虫兆属1新种——周氏颚毛疣虫兆Crossodonthina choui,这是该属在华中地区(湖南)的新记录。新种的正模标本(♂)和2个副模标本(2♂)保存在中南林业科技大学生命科学与技术学院昆虫标本室。     

Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) hydraulic conductivity links to leaf venation architecture under well-watered condition rather than PEG-induced water deficit

Higher plant hydraulic conductivity (K _plant) is vital for plant growth, especially under PEG-induced water deficit stress (PEG-IWDS). Leaf venation architecture is a key determinant of leaf hydraulic conductivity (K _leaf) and K _leaf is a major component of K _plant across different plant species. However, there is little information about (1) varietal difference in leaf vein development in cereal crops, such as rice plants; (2) the effects of PEG-IWDS on leaf vein development; (3) the coordination between leaf venation architecture and K _plant as well as K _leaf under PEG-IWDS. In the present study, widely cultivated eight rice cultivars were grown hydroponically under well-watered condition (WWC) and PEG-IWDS, simulated by adding 15 % (w/v) PEG6000. Leaf venation architecture, including total longitudinal leaf vein number, leaf vein numbers per unit width (LVNW), vein thickness and leaf mass per area, as well as K _plant and K _leaf were measured to address above-mentioned questions. The results showed that leaf venation architecture exhibited significant varietal differences and PEG-IWDS significantly increased LVNW while decreased vein thickness. PEG-IWDS suppressed both K _plant and K _leaf but the decrease was much higher in K _plant than K _leaf. There was a significant and positive correlation observed between LVNW and K _leaf under both WWC and PEG-IWDS but the correlation between LVNW and K _plant was only significant under WWC. K _leaf was significantly and positively correlated with K _plant under WWC but not under PEG-IWDS. It is concluded that K _leaf is a major determinant for K _plant under WWC but not under PEG-IWDS; therefore, breeding or selecting rice cultivars with high LVNW can improve shoot water supplement under WWC but not under PEG-IWDS condition.     

Changes in the Chlorophyll Content and Cytokinin Levels in the Top Three Leaves of New Plant Type Rice During Grain Filling

This paper reports the ways that the differences in leaf senescence are related to grain filling, grain yield, and the dynamics of cytokinins (CKs) in the top three leaves of four field-grown new plant type (NPT) rice, a tropical japonica developed at the International Rice Research Institute, Philippines, to increase the yield potential of rice. The chlorophyll content in leaves decreased from flowering to maturity in all the NPT lines, whereas the grain filling percentage was higher in the fast-senescing NPT line than in slow-senescing NPT line. Grain yield was positively correlated with senescence in the flag leaf. Rapid changes in the CK levels were recorded in the leaves of the fast-senescing line, whereas the CK levels were relatively stable in leaves of the slow-senescing line, suggesting that the dynamics of CKs in the fast-senescing line are vital for fast senescence. There were no significant changes in bioactive CKs, CK O-glucosides (storage CKs), and cis-zeatin derivatives in different leaves of the slow-senescing NPT line between 0 and 3 weeks after flowering, suggesting that the content of these CKs is relatively stable during grain filling. A progressive increase in levels of bioactive CKs was positively correlated with gradual accumulation of CK N-glucosides (inactive CKs) in the top three leaves of the slow-senescing NPT line, whereas the decrease of bioactive CKs in the flag leaf of the fast-senescing line was accompanied by accumulation of CK O-glucosides. These results suggest that there is a higher rate of biosynthesis and/or import of bioactive CKs as well as their turnover which may favor delay of leaf senescence in the slow-senescing NPT line.     

Effects of season-dependent irradiance levels and nitrogen-deficiency on photosynthesis and photoinhibition in field-grown rice (Oryza sativa)

Photoinhibition and acclimation of photosynthesis in rice plants grown under N-sufficient (NS) and N-deficient (ND) field conditions were investigated during the tropical wet (WS) and dry (DS) seasons in the Philippines. Diurnal patterns of CO₂ assimilation were examined. There was a transient peak in CO₂ assimilation in the leaves of the NS plants in the early morning during the DS and the WS, which was not seen in the ND plants in either season. ND leaves had lower Ribulose bisphosphate carboxylase/oxygenase (Rubisco) contents and lower chlorophyll contents. A lowered quantum yield of photosystem II (φPSII) was observed in the ND plants at an intermediate irradiance though no differences between N treatments were seen at high irradiance. Analysis of carotenoids indicated a small increase in the de-epoxidation state of the xanthophyll cycle (DES) at mid-day in the ND leaves compared to NS. Photoinhibition was greater in ND leaves when incident mid-day irradiance was increased by altering the leaf angle. Although Rubisco contents were lower in ND plants, photosynthesis in situ did not decline proportionally. For NS plants, Chlorophyll content, but not Rubisco content, was season-dependent and results are discussed in terms of the interaction between irradiance use and N content of rice leaves.     

Limiting factors for panicle photosynthesis at the anthesis and grain filling stages in rice (Oryza sativa L.)

Panicle photosynthesis is crucial for grain yield in cereal crops; however, the limiting factors for panicle photosynthesis are poorly understood, greatly impeding improvement in this trait. In the present study, pot experiments were conducted to investigate the limiting factors for panicle photosynthesis at the anthesis stage in seven rice genotypes and to examine the temporal variations in photosynthesis during the grain filling stage in the Liangyou 287 genotype. At the anthesis stage, leaf and panicle photosynthesis was positively correlated with stomatal conductance and maximum carboxylation rate, which were in turn associated with hydraulic conductance and nitrogen content, respectively. Panicle hydraulic conductance was positively correlated with the area of bundle sheaths in the panicle neck. During grain filling, leaf and panicle photosynthesis remained constant at the early stage but dramatically decreased from 8 to 9 days after anthesis. The trends of variations in panicle photosynthesis were consistent with those in stomatal conductance but not with those in maximum carboxylation rate. At first, the maximum carboxylation rate and respiration rate in the panicle increased, through elevated panicle nitrogen content, but then drastically decreased, as a result of dehydration. The present study systematically investigated the limiting factors for panicle photosynthesis, which are vital for improving photosynthesis and crop yield.     

Influence of supplemental ultraviolet-B on indoleacetic acid and calmodulin in the leaves of rice (Oryza sativa L.)

IR68 and Dular rice cultivars were grown under ambient, 13.0 (simulating 20% ozone depletion) and 19.1 (simulating 40% ozone depletion) kJ m^-2 day^-1 of biologically effective ultraviolet-B (UV-B_BE) for 4 weeks. Plant height and leaf area were significantly reduced by supplemental UV-B_BE radiation. Greater reduction in leaf area than of plant height was observed. A decrease in indole-3-acetic acid (IAA) content and increase in peroxidase and IAA oxidase activities of UV-B treated plants in both cultivars were observed compared with ambient control. Calmodulin content also decreased after plants were treated with high supplemental UV-B for two weeks and medium UV-B treatment for four weeks. The results indicated that peroxidase and IAA oxidase activities in rice leaves were stimulated by supplemental UV-B, resulting in the destruction of IAA which in turn may cause inhibition of rice leaf growth. Although the mechanism is unclear, calmodulin is most likely involved in leaf growth.