Effect of soil moisture on leaf ecophysiology of <Emphasis Type="Italic">Parasenecio yatabei</Emphasis>, a summer-green herb in a cool–temperate forest understory in Japan

Leaf physiological and gas-exchange traits of a summer-green herbaceous perennial, Parasenecio yatabei, growing along a stream were examined in relation to leaf age. In its vegetative phase, the aerial part of this plant consists of only one leaf and provides an ideal system for the study of leaf longevity. Volumetric soil water content (SWC) decreased with increasing distance from the stream, whereas relative light intensity was nearly constant. The light-saturated net CO₂ assimilation rate (A _sat) and leaf stomatal conductance (gs) were approximately 1.5-fold and 1.4-fold higher, respectively, in the lower slope near the mountain stream than in the upper slope far from the mountain stream. The lifespan of aerial parts of vegetative plants significantly increased with decreasing SWC. The leaf mass-based nitrogen content of the leaves (N _mass) was almost constant (ca. 2.2%); however, the maximum carboxylation rate by ribulose-1,5-biphosphate carboxylase/oxygenase (rubisco) (V _cmax) and photosynthetic nitrogen use efficiency (PNUE, A _sat/N _area) decreased more slowly in the upper slope than in the lower slope. The higher leaf photosynthetic activity of P. yatabei plants growing lower on the slope leads to a decrease in V _cmax and PNUE in the early growing season, and to a shorter leaf lifespan.     

In vivo nitrate reductase activities in different organs of lucerne plants: Effects of combined nitrogen during first vegetative growth and after shoot harvest

Nitrate reductase (EC 1.6.6.1–3; NR) activity was evaluated in nodulated lucerne ( Medicago sativa L. cv. Europe) grown aeroponically in both the presence and absence of applied nitrogen. Determination of in vivo NR activity was done with organ pieces in 0.1 M K⁺-phosphate, pH 7.5, 0.1 M KNO₃ and 1% n -propanol. NR activity was detected in all plant parts. Leaves accounted for 40% of the whole plant activity. Root activity was as high as leaf activity. Stem NR activity accounted for 14 to 20% of the total plant activity. NR activity was also detected in symbolically dependent plants grown without combined nitrogen. Nodule NR in symbolically dependent plants accounted for 17% of the tolal plant aclivity. When nitrate was present in the nulrienl medium, NR increased 5-fold as compared lo N₂-dependenl plants. Varying levels of nitrale (1.65 to 4 m M ) had no influence on leaf or stem activities. However, root NR activity seemed to be related to the nitrale concentration in the nulrient medium. Throughoul inilial vegelative growth, in vivo NR and nitrogenase (acelylene reduction) increased simultaneously. After shoot harvest, nitrogenase (acetylene reduction) aclivity drastically decreased with reduction of photosynthate supply, whereas NR increased in all organs, especially in N₂-dependenl plants.     

中国连香树科的系统研究——Ⅰ.叶的宏观结构及叶柄维管束变化

本文研究了连香树科(Cercidiphyllaceae)叶的宏观结构,首次报道连香树齿腺体显微结构及晶体类型,并对叶柄维管束的变化作了进一步研究。通过与近缘科的比较,我们认为连香树科的系统演化处于孤立地位,和金缕梅科有较近的亲缘关系,与木兰科较为疏远。     

New roles for acyl-CoA-binding proteins (ACBPs) in plant development, stress responses and lipid metabolism

ACBPs are implicated in acyl-CoA trafficking in many eukaryotes and some prokaryotes. Six genes encode proteins designated as AtACBP1-AtACBP6 in the Arabidopsis thaliana ACBP family. These ACBPs are conserved in the acyl-CoA-binding domain, but vary in size from 92 amino acids (10.4 kDa) to 668 amino acids (73.1 kDa), and are subcellularly localised to different compartments in plant cells. Results from in vitro binding assays show that their corresponding recombinant proteins exhibit differential binding affinities to acyl-CoA esters and phospholipids, implying that these ACBPs may have non-redundant biological functions in vivo. By using knockout/downregulated and overexpression lines of Arabidopsis ACBPs, recent investigations have revealed that in addition to their proposed roles in phospholipid metabolism, these ACBPs can influence plant development including early embryogenesis and leaf senescence, as well as plant stress responses including heavy metal resistance, oxidative stress, freezing tolerance and pathogen resistance. In this review, recent progress on the biochemical and functional analyses of Arabidopsis ACBPs, their links to metabolic/signalling pathways, and their potential applications in development of stress tolerance are discussed.     

Leaf ultrastructure of C4 species possessing different Kranz anatomical types in the cyperaceae

The leaf ultrastructure of NADP-malic enzyme type C₄ species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics basically similar to the NADP-malic enzyme group of C₄ grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess such particular membrane systems. The suberized lamella, probably a barrier for CO₂ diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C₄ acids. These ultrastructural features are discussed in relation to C₄ photosynthetic function.     

Retention of xenobiotics along the phloem path

Detached leaves of Cyclamen persicum Mill. can be used as a simple source-sink system. Phloem transport in the excised material was monitored by the noninvasive ¹¹C-technique. Assimilate movement stopped immediately when the petiole was cut off. However, within 20 min a recovery of transport was observed. The translocation rate in the detached leaf was only 13% of that in the intact plant. ¹⁴C-Xenobiotics and [³H]sucrose were injected into the upper petiole parenchyma (source). They moved downstream by a symplastic route. The stump of the petiole was inserted into a buffer solution containing ethylenediaminetetraacetic acid (sink). After 3 h, the distribution of sucrose and xenobiotics was determined in five subsequent segments of the petiole (path). The retention coefficient (r) was calculated from the ratio of radioactivity in the vascular bundle to that in the petiole parenchyma. The distribution along the vascular path was given by a geometric progression, whereas its constant was the transport coefficient (q). Values of r and q corresponded with the degree of phloem mobility and ambimobility. Four groups of compounds were classified: (i) acidic substances with log K_ow = — 2 to — 2.4 (K_ow is the partition coefficient octanol/water) at pH 8 (pH of sieve tube sap), retained by ion trapping and exhibiting small lateral efflux (q0.7; maleic hydrazide, dalapon); (ii) acidic substances with log K_ow = — 0.7 to — 0.8 at pH 8, retained by ion trapping and subjected to a moderate lateral efflux (0.7>q> 0.5; 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, bromoxynil); (iii) nonionised substances retained by optimum permeability, exhibiting a considerable lateral leakage (q<0.5; glyphosate, amitrole); (iv) substances without basipetal transport in the phloem (atrazine, diuron). Retention of sucrose corresponded quantitatively with that shown in group (i). This classification was also supported by results of uptake and efflux experiments using the isolated conducting tissue. Theoretical translocation profiles were calculated from the determined transport coefficients (q).Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - K_ow partition coefficient octanol/water - MCPA 2-methyl-4-chloro-phenoxyacetic acid - q transport coefficient in the vascular bundle - r retention coefficient in the vascular bundle The authors gratefully acknowledge the assistance of H. Fiedler and M. Neugebauer. We are particularly grateful to K. Dutschka, G. Hudepokl, and Dr. J. Knust for producing ¹¹CO₂.     

赤(瓜包)亚族植物叶片中脉的比较解剖

本文对赤(瓜包)属(Thladiantha Bunge)、白兼果属(Baijiana A.M.Lu et J.Q.Li)和苦瓜属(Momordica L.)共11种植物叶片中脉进行了比较解剖学研究。除苦瓜属一种外,其余10种的叶片中脉解剖学资料均为首次报道。分析结果表明:叶片中脉维管束的数目以及排列方式具有分类学意义,而种间和种内维管束数目的减少,在一定程度上反映出植物迁移和演化的方向。     

Dry matter and nutrient inputs through litter fall in a dry tropical forest of India

The present paper elucidates the pattern of leaf and non-leaf fall and quantifies of the total annual input of litter in a dry tropical forest of India. In addition, concentration of selected nutrients in various litter species and their annual return to the forest floor are examined. Total annual input of litter measured in litter traps ranged between 488.0–671.0 g m^-2 of which 65–72% was leaf litter fall and 28–35% wood litter fall. 73–81% leaves fall during the winter season. Herbaceous litter fall ranged between 80.0–110.0 g m^-2 yr^-1. The annual nutrient return through litter fall amounted (kg ha^-1): 51.6–69.6 N, 3.1–4.3 P, 31.0–40.0 Ca, 14.0–19.0 K and 3.7–5.0 Na, of which 71–77% and 23–29% were contributed by leaf and wood litter fall, respectively for different nutrients. Input of nutrients through herbaceous litter was: 13.0–16.6 for N, 1.0–1.4 for P, 4.0–5.0 for Ca, 7.9–10.5 for K and 0.8–1.0 kg ha^-1 yr^-1 for Na.     

Leaf photosynthetic traits scale with hydraulic conductivity and wood density in Panamanian forest canopy trees

We investigated how water transport capacity, wood density and wood anatomy were related to leaf photosynthetic traits in two lowland forests in Panama. Leaf-specific hydraulic conductivity (k_L) of upper branches was positively correlated with maximum rates of net CO₂ assimilation per unit leaf area (A_area) and stomatal conductance (g_s) across 20 species of canopy trees. Maximum k_L showed stronger correlation with A_area than initial k_L suggesting that allocation to photosynthetic potential is proportional to maximum water transport capacity. Terminal branch k_L was negatively correlated with A_area/g_s and positively correlated with photosynthesis per unit N, indicating a trade-off of efficient use of water against efficient use of N in photosynthesis as water transport efficiency varied. Specific hydraulic conductivity calculated from xylem anatomical characteristics (k_theoretical) was positively related to A_area and k_L, consistent with relationships among physiological measurements. Branch wood density was negatively correlated with wood water storage at saturation, k_L, A_area, net CO₂ assimilation per unit leaf mass (A_mass), and minimum leaf water potential measured on covered leaves, suggesting that wood density constrains physiological function to specific operating ranges. Kinetic and static indices of branch water transport capacity thus exhibit considerable co-ordination with allocation to potential carbon gain. Our results indicate that understanding tree hydraulic architecture provides added insights to comparisons of leaf level measurements among species, and links photosynthetic allocation patterns with branch hydraulic processes.