Ear photosynthesis, carbon isotope discrimination and the contribution of respiratory CO2 to differences in grain mass in durum wheat

The role of ear photosynthesis in grain filling was studied in a number of durum wheat (Triticum turgidum var durum L.) landraces and varieties from the Middle East, North Africa, and from the collections of ‘Institut National de la Recherche Agronomique’ (INRA, France) and ‘Centro International de Mejora de Maiz y Trigo’ (CIMMYT, Mexico). Plants were grown in the field in a Mediterranean climate. Flag leaves (blade plus sheath) and ears were kept in the dark from 1 week after anthesis to maturity which reduced grain weight by 22.4% and 59.0%, respectively. In a further experiment, the carbon isotope discrimination ratio (Δ) of ear bracts, awns and flag leaves was measured on samples taken at anthesis and on mature kernels. The mean value of Δ for the water soluble fraction of bracts (17.0‰) and awns (17.7‰) were lower than those of leaves (19.5‰) and fairly similar to those of kernels (17.4‰) averaged across all genotypes. Data indicate that most of the photosynthates in the grain come from ear parts and not from flag leaves. In addition, a higher water use efficiency (WUE) of ear parts than of the flag leaf is suggested by their lower Δ values. Gas exchange in ears and flag leaves was measured during grain filling. Averaged over all genotypes, CO₂ diffusive conductance was about five times higher in the flag leaf than in the spike (with distal portions of awns outside the photosynthetic chamber) 2 weeks after anthesis. In absolute terms, the dark respiration rate (R_d) was greater than the net photosynthesis rate (P_n) by a factor of 1.74 in the spike, whereas R_d was much smaller, only 22.1, 65.7 and 24.8% of P_n in blade, sheath and awns, respectively. Data indicate that photosynthesis, and hence the water use efficiency (photosynthesis/transpiration), is greatly underestimated in ears because of the high rates of respiration which diminish the measured rates of net CO₂ exchange. Results of ¹³C discrimination and gas exchange show that genotypes from North Africa have higher WUE than those from the Middle East. The high R_d values of ears as well as their low diffusive conductance suggest that CO₂ from respiration may be used as source of carbon for ear photosynthesis. In the same way, the anatomy of glumes, for example, supports the role of bracts using internal CO₂ as source of photosynthesis. In the first experiment, the Δ in mature grains from culms with darkened ears compared with control culms provided further evidence in support of this hypothesis. Thus, the Δ from kernels of control plants was 0.40 higher than that from ear-darkened plants, probably because of some degree of refixation (recycling) of respired CO₂ in the grains.     

Neurons projecting from the brain to the corpora allata in orthopteroid insects: anatomy and physiology

Retrograde and orthograde labeling of neurons projecting to the corpus allatum was performed in locust, grasshopper, cricket, and cockroach species in order to identify brain neurons that may be involved in the regulation of juvenile hormone production. In the acridid grasshopper Gomphocerus rufus L., and the locusts Locusta migratoria (R.&F.) and Schistocerca gregaria Forskal, the corpora allata are innervated by two morphologically distinguishable types of brain neurons. One group of 9–13 neurons (depending on species) with somata in the pars lateralis extend axons via the nervus corporis cardiaci 2 and nervus corporis allati 1 to the ipsilateral corpus allatum, whereas two cells in each pars lateralis have bilateral projections and innervate both glands. No direct connection between the pars intercerebralis and corpus allatum has been found. In contrast, neurons with paired axons innervating both glands are not present in Periplaneta americana (L.) and Gryllus bimaculatus de Geer. Instead, two cells in each pars lateralis project only to the gland contralateral to their somata. Electrophysiological experiments on acridid grasshoppers have confirmed the existence of a direct conduction pathway between the two glands via the paired axons of four cells that have been identified by neuroanatomy. These cells are not spontaneously active under experimental conditions. Ongoing discharges in the left and right nerves are unrelated, suggesting that the corpora allata receive independent neuronal inputs from the brain.     

Arrangement of sperm within the spermatheca of fleas, with remarks on sperm displacement

The arrangement of sperm within the spermatheca of the impregnated rabbit flea is described. The numerical superiority of the sperm injections from the numerous later matings suggests that a modified form of sperm displacement probably occurs in this species.     

The effect of water stress on the activities of key regulatory enzymes of the sucrose to starch pathway in wheat

Developmental changes in the starch and sucrose content of grains andthe activities of enzymes of starch synthesis in wheat were studied under waterstress conditions. Water stress caused a marked reduction in the sucrose andstarch content of the grains. Sucrose synthase (SS) and UDP-glucosepyrophosphorylase (UDP-Gppase), showed higher catalytic activity and moreresistance to water stress compared with amyloplastic enzymes. ADP-glucosepyrophosphorylase (ADP-Gppase) activity was reduced to a low level under bothin situ and osmotic stress conditions in which grainsfailed to accumulate dry matter in vivo. Granule-boundstarch synthase (GBSS) also responded rapidly to in situwater stress treatments as did ADP-Gppase. Reduction in GBSS activity at thetime of growth cessation in situ was less than that ofADP-Gppase and the enzyme did not respond to severe osmotic stress. Solublestarch synthase (SSS) was the enzyme most sensitive to water stress in that itresponded earlier, and to a greater extent, than the other enzymes. However,under severe dehydration conditions, leading to cessation of growth, thedeclinein SSS activity was less than that for ADP-Gppase. SSS showed the lowestin vitro activity followed by GBSS. These results suggestthat SSS is the site of response to water stress by which the rate of graingrowth can be affected, whereas growth cessation is due mainly to theinactivation of ADP-Gppase.     

Grain filling pattern and cytokinin content in the grains and roots of rice plants

Grain filling patterns and their relationships withzeatin (Z), zeatin riboside (ZR), indole-3-acetic acid(IAA) and gibberellin (GA) contents in the grains androots during grain development were examined in sixrice (Oryza sativa L.) genotypes grown in thefield and in water culture. Three grain fillingpatterns based on the filling rate of superior andinferior spikelets were observed, i.e., fastsynchronous: all spikelets started filling early andfast at the early filling stage; slowsynchronous: all spikelets filled slowly at the earlyfilling stage and reached the maximum filling ratelate; and asynchronous: superior spikeletsstarted filling and reached the maximum filling ratemuch earlier than the inferior ones. The order ofgrain filling percentage in the three types of grainfilling patterns was: fast synchronous >asynchronous > slow synchronous. Changes in Z + ZRcontents in the superior and inferior spikelets wereassociated with the grain filling patterns. Grainfilling percentage was significantly correlated withZ + ZR contents in the grains and roots at the earlyand middle grain filling stages. IAA and GA(GA¹ + GA³ + GA⁴)contents in the grains and roots were notsignificantly correlated with grain fillingpercentage. The results suggest that cytokinins in thegrains and roots during the early phase of graindevelopment play an important role in regulating grainfilling pattern and consequently influence grainfilling percentage.     

Timing of maturation and the mating system of the spider,Stegodyphus lineatus (Eresidae): how important is body size?

Selection on life history traits such as the timing of maturation and the size at maturity strongly depends on the mating system. In spiders, the mating system hypothesized to Be determined by spermathecal morphology and the related sperm precedence pattern. In a natural population of the eresid spider Stegodyphus lineatus , predictions concerning the timing of maturation, male mating behaviour and success were tested. Eresid spiders are supposed to show protandry, prematuration mate guarding and strong male-male competition resulting in selection for large body size and early maturation. In contrast to these predictions, male and female maturation overlapped largely. Males did not guard premature females nor was there evidence for male-male competition. Among mating pairs, male did not relate to female size, nor to duration of cohabitation. Evidence for an advantage of first over second or large over small males is weak. In males, body size at maturity and the time of maturation were negatively correlated although a trade off between timing of maturation and the body size reached by then should result in a positive correlation. Possible causes are discussed.     

The parameters of grain filling and yield components in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and durum wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L. var. <Emphasis Type="Italic">durum</Emphasis>)

Final grain dry weight, a component of yield in wheat, is dependent on the duration and the rate of grain filling. The purpose of the study was to compare the grain filling patterns between common wheat, (Triticum aestivum L.), and durum wheat, (Triticum turgidum L. var. durum), and investigate relationships among grain filling parameters, yield components and the yield itself. The most important variables in differentiating among grain filling curves were final grain dry weight (W) for common wheat genotypes and grain filling rate (R) for durum wheat genotypes; however, in all cases the sets of variables important in differentiating among grain filling curves were extended to either two or all three parameters. Furthermore, in one out of three environmental conditions and for both groups of genotypes, the most important parameter in the set was grain filling duration (T). It indicates significant impact of environmental conditions on dry matter accumulation and the mutual effect of grain filling duration and its rate on the final grain dry weight. The medium early anthesis date could be associated with further grain weight and yield improvements in wheat. Grain filling of earlier genotypes occurs in more temperate environments, which provides enough time for gradual grain fill and avoids the extremes of temperature and the stress of dry conditions.     

干旱胁迫对小麦旗叶活性氧代谢及灌浆速率的影响

在防雨池栽条件下,研究了干旱胁迫对小麦旗叶活性氧代谢的影响.结果表明,小麦旗叶内H2O2和O-·2水平随干旱胁迫的加剧和衰老进程的加快而逐渐升高,活性氧清除系统中的SOD和CAT活性逐渐下降,膜脂过氧化产物MDA含量升高,导致叶片内可溶性蛋白质和叶绿素含量下降,是干旱胁迫造成对籽粒产量贡献较大的旗叶伤害的主要原因之一,从而导致穗粒重下降.