禄丰古猿化石地点的植物叶化石

1987年,在云南禄丰古猿化石地点D剖面第4层(薄层黑色炭质粘土与灰色细砂互层)发现植物叶部印痕化石,经鉴定属壳斗科绝灭的雷龙潭槲叶(Dryophyllum relongtanense Colani),该种植物常参与组成亚热带至暖温带的常绿阔叶林或常绿与落叶阔叶混交林。     

Import of 14C-Photosynthate by Developing Leaves of Sugarcane

Sink-to-source transition was studied in developing sugarcane (Saccharum interspecific variety L62–96) leaves. Fully-expanded, mature sugarcane leaves were fed ¹⁴CO₂ for 20 minutes, incorporating about 617 Bq. After five hours the leaves of each plant were cut into 1-cm-length segments that were weighed and then placed in scintillation cocktail for counting. All leaves younger than the leaf fed ¹⁴CO₂ imported labeled photoassimilate. Three to four leaves had both importing and non-importing regions within the blade and a distinct transition region between them. A transition region was observed in leaves which had expanded to between 30 and 90 % of final blade length. Radioactivity per gram fresh weight was calculated as a measure of sink strength. Sink strength was greatest in the youngest leaf and declined with leaf age. The results of this study indicate that 1) import of photosynthate by developing sugarcane leaves occurs over a longer span of developmental ages than in dicotyledonous leaves and 2) the actual tissue region undergoing transition within such a leaf can be resolved as narrow zone between the importing and non-importing regions.     

水分胁迫对棉花叶片中IAA从含量、IAA氧化酶和过氧化物酶活性的影响

整株干旱降低盐棉46号叶片中的IAA总量,叶龄愈小下降愈多。幼叶中IAA总量的下降主要是结合态IAA减少的结果。气干和-1.7MPa PEG溶液渗透胁迫处理也降低离体成熟叶片的IAA总量,其变化与叶片含水量呈直线相关(r=0.905)。整株干旱处理提高各叶片的过氧化物酶活性,叶龄愈小提高愈多,但IAA氧化酶活性无显著变化。离体和整株干旱时IAA总量的下降,可能是过氧化物酶活性增加所致。     

DEVELOPMENTAL STABILITY IN LEAVES OF CLARKIA TEMBLORIENSIS (ONAGRACEAE) AS RELATED TO POPULATION OUTCROSSING RATES AND HETEROZYGOSITY

Four natural populations of Clarkia tembloriensis, whose levels of heterozygosity and rates of outcrossing were previously found to be correlated, are examined for developmental instability in their leaves. From the northern end of the species range, we compare a predominantly selfing population (t? = 0.26) with a more outcrossed population (t? = 0.84), which is genetically similar. From the southern end of the range, we compare a highly selfing population (t? = 0.03) with a more outcrossed population (t? = 0.58). We measured developmental stability in the populations using two measures of within-plant variation in leaf length as well as calculations of fluctuating asymmetry (FA) for several leaf traits. Growth-chamber experiments show that selfing populations are significantly more variable in leaf length than more outcrossed populations. Developmental instability can contribute to this difference in population-level variance. Plants from more homozygous populations tend to have greater within-plant variance over developmentally comparable nodes than plants from more heterozygous populations, but the difference is not significant. At the upper nodes of the plant, mature leaf length declines steadily with plant age, allowing for a regression of leaf length on node. On average, the plants from more homozygous populations showed higher variance about the regression (MSE) and lower R² values, suggesting that the decline in leaf length with plant age is less stable in plants from selfing populations than in plants from outcrossing populations. Fluctuating asymmetry (FA) was calculated for four traits within single leaves at up to five nodes per plant. At the early nodes of the plant where leaf arrangement is opposite, FA was also calculated for the same traits between opposite leaves at a node. Fluctuating asymmetry is significantly greater in the southern selfing population than in the neighboring outcrossed population. Northern populations do not differ in FA. Fluctuating asymmetry can vary significantly between nodes. The FA values of different leaf traits were not correlated. We show that developmental stability can be measured in plants using FA and within-plant variance. Our data suggest that large differences in breeding system are associated with differences in stability, with more inbred populations being the least stable.     

Genetic research as the valid base of strategies for breeding rust resistant wheats

It is known that few wheat cultivars maintain their resistance to rust diseases for a long period of time, particularly when crop populations become genetically more uniform. A number of genetically diverse, so far unexploited, sources of rust resistance in the natural as well as mutagenized population of wheat cultivars were identified. Several of these genes were placed in agronomically superior well-adapted backgrounds so that they could be used as pre-breeding stocks for introducing genetic diversity for resistance in a crop population. Some of these stocks when employed as parents in several cross combinations in a breeding programme have generated a number of promising cultivars with diversity for resistance.Many presently grown wheats in India, near-isogenic lines each with Lr14b, Lr14ab, Lr30 and certain international cultivars were identified as possessing diverse sources of adult plant resistance (APR) to leaf rust. Prolonged leaf rust resistance in some of the Indian cultivars was attributed to the likely presence of Lr34 either alone or in combination with other APR components. Tests of allelism carried out in certain cultivars that continue to show adequate levels of field resistance confirm the presence of Lr34, which explains the role that this gene has played in imparting durability for resistance to leaf rust. Also, Lr34 in combination with other APR components increases the levels of resistance, which suggests that combination of certain APR components should be another important strategy for breeding cultivars conferring durable and adequate levels of resistance. A new adult plant leaf rust resistance source that seems to be associated with durability in Arjun has been postulated. Likewise, cultivars possessing Sr2 in combination with certain other specific genes have maintained resistance to stem rust.Further, non-specific resistances that were transferred across widely different genotypes into two of the popular Indian wheats provided easily usable materials to the national breeding programmes for imparting durable resistance to stripe rust.     

Variable effects of air-drying on leaching losses from tree leaf litter

Leaching of soluble substances may be an important first step in leaf litter decomposition in small streams, but recent research has suggested that large leaching losses (up to 30% of initial mass in 48 h) may be an artifact created by using air-dried leaves in decomposition experiments. In laboratory experiments, we compared 3 d leaching losses from freshly fallen and air-dried senescent leaves of 27 tree species from different regions across Canada. Air-dried leaves from all species leached measurable amounts of original mass (3.6–32.8% dry mass), but leaching losses from fresh leaves (0–35%) were detectable in all but two species. Air-drying increased leaching losses in many species, but in others it reduced leaching losses or had no measurable effect. Results for leaves of the same species collected in different regions or in different years were generally similar, but species within the same genus often behaved very differently. Neither moisture content (fresh or air-dried), leaf thickness, nor cuticle thickness proved of any value as predictors of leaching losses or the effect of air-drying. The propensity of autumn-fallen leaves to leach, whether fresh or air-dried, appears to be a property of the individual tree species.     

Survey of leaf anatomy,especially secretory structures,of tribeCaesalpinieae (Leguminosae,Caesalpinioideae)

We studied leaflet anatomy, emphasizing secretory structures, from herbarium specimens of 128 species of 44 genera of tribeCaesalpinieae, using clearings, resin sections, and scanning electron microscopy. These observations, combined with those from our three earlier papers, provide a survey of 210 species representing all genera. Seventy-three species had secretory structures: 21 had glands or gland-like trichomes, 40 had living mesophyll idioblasts, and nine had cavities (three species each had two different types). Five additional species, all inCercidium (Caesalpinia group), had paired or clustered large spheroidal, thick-walled, empty cells (veinlet idioblasts) interconnected by perforation plate-like gaps. Secretory structures have systematic significance at various taxonomic levels.     

Somatic embryogenesis from immature leaves of in vitro grown tea shoots

Immature leaves of in vitro grown shoots of tea were cultured on various levels of 2,4-D. Somatic embryos were induced directly on leaves or via embryogenic callus produced at the basal regions of the leaves. Induction of embryogenesis appeared to be correlated with the maturity of the leaf explants, with younger leaves responding better. The embryogenic response of leaf explants also was correlated with the period of culture in 2,4-D containing liquid medium. Embryogenic calli or repetitive somatic embryos maintained their regeneration capacity for more than 3 years. Histological observation revealed somatic embryos were formed on various regions of the leaf midrib. Somatic embryos germinated and developed into plantlets on agar medium containing BA and IBA.Abbreviations BA 6-benzylaminopurine - IBA indole-3-butyricacid - 2,4-D 2,4-dichloro phenoxyacetic acid     

Cell wall composition of leaves of an inherently fast- and an inherently slow-growing grass species

Differences in the relative growth rules of the inherently slow-growing Deschampsia flexuosa L. and the inherently fast-growing Holcus lanatus L. were reflected in cell wall synthesis in the elongation zone of the leaves. Leaf elongation rates depended on the size of the plant and ranged from 6 to 14 mm d^?1 in Deschampsia and from 12 to 42 mm d^?1 in Holcus. Anatomical data showed that the epidermis and vascular tissue are the important tissues controlling leaf extension. The cell wall polysaccharides of fully expanded leaves of the two species were identical in sugar composition. Enzymatic hydrolysis of polymeric sugars in the cell walls of the sheath and the lamina gave glucose (85%), arabinose (3.5%), fucose (0.5%), xylose (5.0%), mannose (0.5%), galaclose (0.8%) and galacturonic acid (3–4%). This composition applied throughout the blade and the sheath and did not change with ageing. Polysaccharides in the meristems of the two species showed identical sugar compositions with 51–55% glucose, 13–15% galactoronic acid and 13–14% arabinose as the main components. The extension zone was marked by a gradual increase of driselase-digestable polymers (per mm tissue) and a concurrent shift in sugar composition. The massive increase of glucose in the cell wall polymers of the elongation zone is probably caused by cellulose synthesis. The rate of synthesis of cell wall polysaccharides in Holcus was twice as high as that in Deschampsia. The slower-growing Deschampsia has more ferulic acid esterified with cell walls, which might contribute to the slowing of leaf growth. Lignin is not significantly deposited until growth has essentially ceased and is not responsible for the difference in growth rate.