祁连山海北高寒草甸地区UV-B的气候变化特征

分析祁连山海北高寒草甸地区2002年太阳总辐射（Eg）、UV-B及UV-B占Eg比例的气候变化特征。结果表明：海北站地区UV-B较强，日瞬时最高接近10W•m^-2，日总量最高达0．204MJ•m^-2；日、年变化依Eg的日、年变化具有显著的正相关关系。UV-B与Eg的比值（η），不论是日变化还是年变化表现明显，一日间早晚低，中午高，一年间6月最高，冬季的12月低，与太阳高度角的变化具有一定的正相关关系。年平均η约为0．54％，植物生长期的5～9月约为0．65％。在海北高寒草甸地区Eg和UV-B的年总量分别达6387．436MJ•m^-2和35．981MJ•m^-2。

长期增强UV-B辐射对高寒草甸植物光合速率和抗氧化系统的影响

研究了在野外自然条件下，长期增强UV-B辐射对高寒草甸3种典型植物矮嵩草（Kobresia humilis）、垂穗披碱草（Elymus nutans）和钉柱委陵菜（Potentilla saundersiana）光合放氧速率、光合色素和抗氧化系统的影响。结果表明：长期增强UV-B辐射对3种植物的净光合速率没有明显影响。增强UV-B辐射下，3种植物的叶绿素含量变化不同，Chla／b值，类胡萝卜素（Car）含量，Car／Chl值与对照相比都有升高，说明植物叶片的光合能力、吸收紫外线的能力增强以及忍受逆境能力均有增强，从而产生光保护，有利于光合作用正常进行。由于3种植物膜脂过氧化程度的不同及SOD活性的普遍抑制，植物经受了氧化胁迫。垂穗披碱草叶片GSH含量显著七升，矮嵩草的形态矮小及钉柱委陵菜GSH含量与POD活性显著上升，都能减轻它们所经受的氧化胁迫，使光合器官免受损伤。所以，这些保护性色素的积累和抗氧化系统内部的协同作用可能是高寒草甸植物光合作用正常进行的重要原因。

增强UV-B辐射对麻花艽叶片的抗氧化酶的影响

以青藏高原的特有植物麻花艽为材料,研究麻花艽叶片抗氧化酶系统对增强UV-B辐射的响应.结果表明:在UV-B处理初期,麻花艽叶片SOD、POD的酶活性都能增加,但随着处理时间的延长,SOD、POD的活性呈现下降趋势.麻花艽叶片CAT的酶活性在UV-B处理后下降明显,但作为清除叶绿体中H2O2的关键酶AP的酶活性表现为明显地增加趋势,说明在对麻花艽叶片增强UV-B辐射反应中AP起有着重要作用.MDA的含量随UV-B处理时间延长而增加,表明UV-B降低了细胞内活性氧自由基的清除能力,膜脂过氧化作用加剧,导致了对麻花艽叶片的伤害效应.

不同强度的UV-B辐射对高山植物麻花艽光合作用及暗呼吸的影响

以人工种植的多年生高山植物麻花艽( Gentiana straminea )为材料,在3个不同强度的UV-B辐射处理下,定时测定处理和对照叶片的净光合速率、表观量子效率和暗呼吸的变化.结果显示:UV-B处理对麻花艽叶片的光合作用在短期内有一定的抑制作用,但随着处理时间的增加,该高山植物能很快地适应强UV-B辐射的处理.表明麻花艽这种青藏高原常见的高山植物在长期的自然选择过程中可能已经形成了适应UV-B辐射的特有生理机制.暗呼吸的实验结果亦表明:在3种强度的UV-B辐射处理下,麻花艽叶片的呼吸作用从一开始就未受到抑制;随着UV-B辐射时间的增加,UV-B辐射强度越高,呼吸强度越强;这可能是 UV-B辐射并未引起麻花艽呼吸机构的破坏所致.

UV－B辐射增强对植物光合作用的影响及植物的相关适应性研究

综述了UV－B辐射增强对植物光合作用的影响、植物对光破坏的响应与适应性方面的国内外研究进展，许多研究表明UV－B辐射增强对植物具有破坏作用且能引起植物光抑制、光氧化和光损伤，植物依靠自身修复系统而对其破坏又具有一定的适应性。

增强UV-B辐射对高山植物麻花艽净光合速率的影响

在高寒矮嵩草 (K obresia humilis)草甸地区以太阳短波辐射为背景 ,建立了人工增强 U V- B辐射的实验装置 ,每天增补 15 .8k J· m- 2 的辐射剂量 ,模拟平流层臭氧破坏约 5 %时近地表面太阳 UV- B辐射的增强。观测表明 :UV- B辐射的增强对麻花艽 (Gentiana straminea)植物的光合作用无明显的抑制或伤害作用。相反 ,在早晨补充UV- B辐射的短时间内 ,叶片的 Pn 随 Gs的增大而有所提高。随 UV- B辐射时间的延长 ,约在 11∶ 30～ 12∶ 30 ,Pn和Gs有所降低。U V- B辐射时间进一步延长后 (约 14∶ 0 0以后 ) ,处理和对照组叶片 Pn和 Gs的差异趋向不明显。增强太阳 UV- B辐射后 ,麻花艽叶片的光合色素并无明显变化 ,U V-B 吸收物质的含量也无明显变化。麻花艽叶片厚度的直接测量表明: 增强UV -B 辐射能明显提高叶片的厚度。叶片厚度的增加可补偿增强UV -B 辐射后引起的光合色素的光降解, 改善单位叶面积为基础的光合速率, 是高原植物对强UV-B 辐射的一种适应方式。

不同海拔地区紫外线B辐射状况及植物叶片紫外线吸收物质含量的分析

对不同海拔地区的太阳 UV- B辐射和植物叶片的光学特性进行了比较研究。结果表明 :位于高海拔地区的海北高寒草甸生态系统定位站 ,太阳 UV- B辐射明显高于相近纬度的西宁、兰州和南京地区。UV- B辐射与总辐射和 PAR的日变化规律相似 ,都受太阳高度角的直接影响 ,在当地太阳正午时最高。UV- B/Q的日变化也为单峰曲线 ,海北站地区的 UV- B/Q高于西宁的同期测定结果。对珠芽蓼等植物的研究表明 ,生长于海北站地区的珠芽蓼 ,其叶片中紫外线吸收物质的含量明显高于西宁的同种植物 ,也略高于海拔较高的达坂山和小达坂山山顶的同种植物。叶绿素含量以海北站珠芽蓼最低 ,达坂山和小达坂山的同种植物最高。珠芽蓼叶片中类胡萝卜素的含量以西宁最低, 海北站、达坂山和小达坂山依次升高。海北站矮嵩草与从海北站移植到西宁生长4年的同种植物相比, 叶片中紫外线吸收物质、叶绿素、类胡萝卜素的变化与生长于两地区的珠芽蓼相同。

增强的UV-B辐射对黄瓜（Cucumis sativus）不同叶位叶片生长、光合作用和呼吸作用的影响

在植物生长室中 ,黄瓜植株第 1片真叶出现后 ,用人工UV B光源照射 6 0d ,测定植物各叶位叶片的生长和生理活动 .结果表明 ,UV B辐射条件下 ,植物出叶时间被延迟 ;叶面积和叶干重下降 ,降幅与叶位高低正相关 ;叶片含水量降低 ,老龄叶片 (第 1叶 ,下位叶 )和幼龄叶片 (第 5叶 ,上位叶 )的水分降幅均高于成年叶片 (第 3叶 ,中位叶 ) ;叶片的伸展速度、叶片数目以及单叶面积减少 ,致使黄瓜总叶面积下降 ;植株节间长度缩短 ,是植株矮化的重要原因 ;根、茎、叶等器官之间的相关生长变化不大.叶片生长在其中起重要的协调作用. UV-B 降低Pn和EAQE ,对光合作用的抑制程度随叶位升高而增加. UV-B 辐射后,黄瓜叶片的光呼吸显著提高,增幅与叶片发育阶段有关. UV-B 对黄瓜第1叶的暗呼吸没有影响,第2 、3 叶略微下降,第4 叶显著升高. 分析认为,植株矮化和叶面积减少有利于植物适应UV-B辐射;水分含量和光合作用减少、呼吸作用增强是黄瓜生长受抑制的生理基础。

UV-B辐射对大豆和黄瓜幼苗某些生理特性的影响

在植物生长室中，UV-B辐射明显降低黄瓜幼苗的根系活力，抑制程度随辐射时间的延长而增强．黄瓜和大豆幼苗的叶绿素和可溶性蛋白含量减少与UV-B辐射时间长短呈正相关，但是类胡萝卜素减少幅度不大．UV-B对Chlb的破坏较Chla严重，导致Chla b比值增大．UV-B虽增加大豆幼苗的SOD活性，但降低大豆幼苗的ＮＲ活性及其对温度变化的敏感性．分析认为，Chlab比值和SOD 活性升高，有助于植物对UV-B的适应。

紫外线—B辐射对3种植物幼苗光合作用和呼吸作用的影响研究初报

UV - B 辐射明显降低大豆、豌豆和黄瓜3 种植物幼苗的净光合速率和量子效率, 降幅随UV - B辐射时间延长而增加, 是一定UV - B 强度下,UV - B 辐射剂量的累积效应。豌豆和大豆幼苗的暗呼吸速率受UV - B 辐射抑制, 其中, 豌豆叶片暗呼吸受抑程度与UV - B 辐射时间正相关。

浅析植物对太阳紫外线-B辐射的适应

Plants have an integral adaptive mechanism to solar UV -B radiation from plant morphology to physiological action and the formation of UV -B radiation absorption pigment is very significant. There is the close interrelation between plant adaptive mechanism and its origin and distribution, which has the profound molecular basis. It is important to strengthen study on the enhancing solar UV _ B radiation instead of being afraid of or optimistic about it in order to solve the uncertainties and make scientific decision.

Dissection of rye B chromosomes, and nondisjunction properties of the dissected segments in a common wheat background

The rye B chromosome is a supernumerary chromosome that increases in number in its host by directed postmeiotic drive. Two types of rye B chromosomes that had been introduced into common wheat were dissected into separate segments by the gametocidal system to produce a number of rearranged B chromosomes, such as telosomes, terminal deletions and translocations with wheat chromosomes. A total of 13 dissected B chromosomes were isolated in common wheat, and were investigated for their nondisjunction. properties. Rearranged B chromosomes, separated from their B-specific repetitive sequences on the distal part of the long arm, did not undergo nondisjunction, and neither did a translocated wheat chromosome carrying a long-arm distal segment containing the B-specific repetitive sequences. However, such rearranged B chromosomes, missing their B-specific sequences could undergo nondisjunction when they coexisted with the standard B chromosome or a wheat chromosome carrying the B-specific sequences. Deficiencies of the short arm did not completely abolish the nondisjunction properties of the B chromosome, but did reduce the frequency of nondisjunction. These results confirmed previous suggestions that the directed nondisjunction of the rye B chromosome is controlled by two elements, pericentromeric sticking sites and a trans-acting element carried at the distal region of the long arm of the B chromosome. Additionally, it is now shown that the distal region of the long arm of the B chromosome which provides this function is that which carries the B-specific repetitive sequences.

Mitochondrial cytochrome b sequence variation and phylogenetics of the highly specialized schizothoracine fishes (Teleostei : Cyprinidae) in the Qinghai-Tibet Plateau

The complete 1140 bp mitochondial cytochrome b sequences were obtained from 39 individuals representing five species of all four genera of highly specialized schizothoracine fishes distributed in the Qinghai-Tibet plateau. Sequence variation of the cytochrome b gene was surveyed among the 39 individuals as well as three primitive schizothoracines and one outgroup. Phylogenetic analysis suggested that the group assignment based on 1140 bp of the cytochrome b sequence is obviously; different from previous assignments, and the highly specialized schizothoracine fishes (Schizopygopsis pylzovi, Gymnocypris przewalskii, G. eckloni, Chuanchia lablosa, and Platypharodon extremus) form a monophyletic group that is sister to the clade formed by the primitive schizothoracine fishes (Schizothorax prenanti, S. pseudaksaiensis, and S. argentatus). The haplotypes of Schizopygopsis pylzovi and G. przewalskii were paraphyletic based on cytochrome b data, which most likely reflected incomplete sorting of mitochondrial DNA lineages. The diploid chromosome numbers of Schizofhoracinae were considered in phylogenetic analysis and provided a clear pattern of relationships. Molecular dating estimated for highly specialized schizothoracine fishes suggested that the highly specialized schizothoracine fishes diverged in the late Miocene Pliocene to Pleistocene (4.5x10(4)-4.05x10(6) Years BP). The relationship between the cladogenesis of highly specialized schizothoracine fishes and geographical events of the Qinghai-Tibet plateau is discussed.

Photosynthesis of Saussurea superba and Gentiana straminea is not reduced after long-term enhancement of UV-B radiation

Experiments were conducted in an alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37degrees29'-37degrees45'N, 101degrees12'-101degrees33'E; altitude 3200 m). Effects of enhanced ultraviolet-B (UV-B) radiation on photosynthesis of the alpine plants of Saussurea superba and Gentiana straminea were investigated. Both species were exposed to a UV-B-BE density at 15.80 kJ m(-2) per day, simulating nearly 14% ozone (O-3) reduction during the plant growing season. Neither photosynthetic CO2 uptake rate nor photosynthetic O-2 evolution rate were decreased after a long period of enhanced UV-B radiation treatment. On the contrary, there was a tendency to increase of both parameters in both species. The photosynthetic pigments were also increased, when expressed on a leaf area basis. UV-B absorbing compounds, detected by the absorbance values at 300 mm, had a tendency to increase in both species after enhanced UV-B radiation. After long-term exposure of plants to enhanced UV-B radiation, leaf morphology was also affected. Leaf thickness in both S. superba and G. straminea were increased significantly (P < 0.001). This supports our hypothesis that the increase of leaf thickness in both species after long-term exposure of enhanced UV-B radiation could compensate for the photodestruction of photosynthetic pigments when light passes through the leaf. Therefore, photosynthesis is not reduced in either species when expressed on leaf area basis. (C) 2003 Elsevier B.V. All rights reserved.