Photosynthetic Capacity and Carbon Contribution of Leaves and Bracts to Developing Floral Buds in Cotton

During ontogeny of Gossypium hirsutum L. floral buds (squares), increases in area and dry mass (DM) of floral bracts and the subtending sympodial leaf followed a sigmoid growth curve with increasing square age. The maximum growth rates of the bract area and bract DM occurred between 15 and 20 d after square first appearance (3 mm in diameter). Net photosynthetic rate (P_N) of the sympodial leaf at first fruiting branch position of main-stem node 10 reached a maximum when the subtended square developed into a white flower. Floral bracts had much lower P_N and higher dark respiration than the subtending leaf. The amount of ¹⁴CO₂ fixation by the bracts of a 20-d-old square was only 22 % of the subtending leaf, but 56 % of ¹⁴C-assimilate in the floral bud was accumulated from the bracts, 27 % from the subtending leaf, and only 17 % from the main-stem leaf at 6 h after ¹⁴C feeding these source s. Hence floral bracts play an important role in the carbon supply of developing cotton squares. This revised version was published online in September 2006 with corrections to the Cover Date.     

Discontinuities in the Temperature Function of Transmembrane Water Transport in Chara: Relation to Ion Transport

The NMR (nuclear magnetic resonance) method of Conlon and Outhred (1972) was used to measure diffusional water permeability of the nodal cells of the green alga Chara gymnophylla. Two local minima at 15 and 30°C of diffusional water permeability (P _d ) were observed delimiting a region of low activation energy (E _a around 20 kJ/mol) indicative of an optimal temperature region for membrane transport processes. Above and below this region water transport was of a different type with high E _a (about 70 kJ/mol). The triphasic temperature dependence of the water transport suggested a channel-mediated transport at 15–30°C and lipid matrix-mediated transport beyond this region. The K⁺ channel inhibitor, tetraethylammonium as well as the Cl⁻ channel inhibitor, ethacrynic acid, diminished P _d in the intermediate temperature region by 54 and 40%, respectively. The sulfhydryl agent p-(chloromercuri-benzensulfonate) the water transport inhibitor in erythrocytes also known to affect K⁺ transport in Chara, only increased P _d below 15°C. In high external potassium (`K-state') water transport minima were pronounced. The role of K⁺ channels as sensors of the optimal temperature limits was further emphasized by showing a similar triphasic temperature dependence of the conductance of a single K⁺ channel also known to cotransport water, which originated from cytoplasmic droplets (putatively tonoplast) of C. gymnophylla. The minimum of K⁺ single channel conductance at around 15°C, unlike the one at 30°C, was sensitive to changes of growth temperature underlining membrane lipid involvement. The additional role of intracellular (membrane?) water in the generation of discontinuities in the above thermal functions was suggested by an Arrhenius plot of the cellular water relaxation rate which showed breaks at 13 and 29°C. Received: 12 August 1998/Revised: 13 November 1998     

Plant Production in Relation to Foliage Illumination

The intensity of light received by plants can be specified interms of its extinction with depth in the foliage. Various light-extinctionfunctions are introduced to specify the light received by plantswith different patterns of foliage development (viz. standardexponential, best exponential, and ideal). The implicationsof these extinction functions are discussed and the productionassociated with each foliage type is studied as a function ofleaf area index, LAI (the ratio of leaf area to ground area).The concepts of optimum LAI and ceiling LAI are considered inrelation to these foliages. It is shown that, contrary to whathas previously been thought, a foliage in which the bottom leavesare at compensation point is not necessarily at optimum LAI.It also becomes possible to reconcile conflicting views on therelationship between optimum LAI and ceiling LAI.     

Water Flow Through Cotton Roots in Relation to Xylem Anatomy

The effect of root anatomy on water flow was studied in 7-d-oldcotton (Gossypium hirsutum L.) seedlings grown in solution culture.The total water flux of the intact root system was measuredusing a pressure chamber. Then successive terminal root sectionswere removed at 2,6,10 and 12 cm behind the root tip and theflux was remeasured after each successive cut was made. Xylemdevelopment at different distances behind the root apex wasstudied with a microscope using sections cut free-hand and stainedwith toluidine blue. Water flux increased with the removal ofsuccessive terminal root sections and this coincided with thedegree of basipetal primary xylem development. The large increasein water flux at 10 to 12 cm was associated with secondary xylemdevelopment and increased xylem vessel number. A comparison of water flow and xylem anatomy between roots withtetrarch (Stoneville 506 and Deltapine 41) and pentarch (T25strain) vascular bundle arrangements showed no significant differencesin the measured values of water flux for the primary root. Waterflux, estimated using Poiseuille's equation and measured xylemdimensions, was greater for the tetrarch roots, primarily becauseof the larger diameter of individual vessel elements. The increasednumber of vessel elements in the pentarch primary root of T25did not result in any apparent decrease in axial resistanceto water flow. Key words: Gossypium hirsutum L., roots, vascular bundle, xylem water flux, xylem     

Storage-protein Deposition in the Developing Rice Caryopsis in Relation to the Transport Tissues

The developing caryopsis of rice (Oryza sativa L.) was examinedhistologically at successive stages of grain-filling in orderto identify the factors which determine the distribution ofstorage protein in the endosperm, and which terminate the depositionof endosperm protein. The storage protein was deposited at theperiphery of the endosperm, and this distribution was apparentlycaused by the radial pattern of cell development in the endosperm,and by the proximity of the peripheral endosperm cells to thenucellar epidermis. The nucellar epidermis directly surroundsthe endosperm and functions as the pathway for amino acid transportto the endosperm. During the later stages of caryopsis developmentthe nucellar epidermis became compressed by being ‘sandwiched’between the expanding endosperm and the rigid hull (the tightlylocked palea and lemma) which encloses the caryopsis. It isproposed that this compression of the nucellar epidermis blocksthe supply of amino acids to the endosperm and thereby terminatesthe deposition of storage protein in the rice grain. Oryza sativa, rice, caryopsis (development), endosperm, grain filling, nucellar epidermis, storage protein     

Morphology and Ultrastructure of Immature Cereal Grains in Relation to Transport

The surfaces of the pericarps of wheat and barley grains, 15–30days after anthesis, were examined. Stomata were found in thepericarp epidermis on the ventral side at the apical end inone variety of wheat and four varieties of barley. Layers whichstained red with Sudan IV were observed on the pericarp epidermisand on either side of the testa in immature barley grains. Theultrastructure of these layers was investigated. It was concludedthat the cuticular layer inside the testa is derived from thenucellus. The significance of these cuticular layers in relationto the supply of carbon dioxide to the photosynthesizing cellsof the pericarp is discussed. The movement of photosynthateand oxygen produced in the pericarp is also considered. Hordeum vulgare L, Triticum aestivum L, barley, wheat, cereal grain, cuticle, stomata, pericarp     

Protein Transport in Plant Cells

The subcellular localization and secretion of proteins synthesized in the cytosol are determined by short amino acid sequences in their molecules. N-terminal transit peptides provide for protein translocation across the membranes of the ER, mitochondria, plastids, and microbodies. Later, these peptides are cleaved off by processing peptidases. C-terminal peptides direct some proteins into microbodies and vacuoles. Transport into the nucleus and insertion in the membranes are determined by the specific sequences that reside in the molecule of the mature protein. Specific receptors associated with the protein-translocating channel recognize transit peptides. Protein unfolding is required for successful protein transport through these channels. Chaperones maintain proteins in such a state. Folded proteins cross the nuclear pore complex and the membrane of microbodies. Protein transport is tightly associated with their processing. During the vesicular protein transport within the endomembrane system (ER, Golgi apparatus, plasma membrane, and vacuoles), correct protein targeting is ensured by protein sorting during vesicle loading, the assembly of corresponding protein coats, vesicle transport to the acceptor membrane, and specific membrane fusion.     

植物中的核质转运相关蛋白

细胞内各个生命过程的有序进行需要生物大分子在细胞核与细胞质之间有选择、有控制地转运.而细胞核膜的存在为大分子的自由穿梭设置了屏障,因此生物大分子在细胞核与细胞质之间的转运要依赖于一些受体蛋白.输入蛋白β(importinβ)是首先从人类细胞中发现的生物大分子向细胞核输入的受体,其后相继鉴定出多个与输入蛋白β具有同源性的细胞核转运受体,命名为类输入蛋白β.这些转运受体介导的转运过程在生物有机体之间高度保守,在动物及酵母中调控核质穿梭以及各个信号过程的组分与分子机制研究较为清楚,但在植物中相对匮乏.本文在介绍细胞核转运受体共有结构特点和转运机制基础上,重点综述了植物细胞核转运受体的最新研究进展以及这些受体在植物信号转导中的重要调节作用.     

Auxin Transport as Related to Leaf Abscission during Water Stress in Cotton

Plant water deficits reduced the basipetal transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of ¹⁴C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetally translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in well watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential sufficient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of well watered petioles tested under anaerobic conditions and acropetal transport tested under all conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maximally reduced is more critical than the degree of reduction.     

风沙移动与植物生物量的关系以及植物固沙能力研究

荒漠化是植被覆盖退化、风蚀水蚀加剧的过程。适应流沙条件的植物能够逆转荒漠化（沙化）过程,能够固沙。可用于研究植物固沙能力的数据不多。为了研究与植物生物量相关的植株周围的“风成沙移置(wind-induced sand diplacement)”,在研究中,将植株周围的风沙移动与3种植物的生物量配置格局联系起来,并发展了一种新方法,以对植物固沙能力进行实验研究,风沙移动与生物量的关系不是线性的。除了植物生物量大小外,种类特异的植物特征,如生物量配置格局和植物枝叶的结构特征,在确定植物固沙能力方面也很重要。     

棉花li突变体生长素极性运输的减弱

陆地棉(Gossypium hirsutum L.)li突变体叶片卷曲,植株扭曲,种子表皮毛明显偏短。通过扫描电子显微镜(SEM)观察发现,li突变体的纤维发育在起始期与野生型植株并无明显差异,但在伸长期开始后,如开花后3d(3 day post anthesis,DPA),纤维伸长受阻;li突变体茎的形成层和韧皮部分化发育不完全,生长素由顶端向基部的极性运输能力下降,仅为野生型植株的大约三分之一。推测棉花li突变体包括纤维发育不良在内的多效性异常表型,与其生长素极性运输能力的下降有关。     

植物芥子油苷代谢及其转移

芥子油苷是一类含氮、含硫的植物次生代谢产物,主要分布于十字花科植物。芥子油苷及其降解产物具有多种生化活性,在植物防御方面也有重要作用。简要介绍芥子油苷的分布、合成、降解和在植物体内的转移。