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The net assimilation rate (EA), relative growth-rate (Rw), andleaf-area ratio (FA) were measured for rape (Brassica napus),sunflower (Hetianthus annuus), and maize (Zea mays) at varioustimes of year in an arid climate, using young plants grown widelyspaced on nutrient culture. Multiple regression analysis accountedfor 9095 per cent of the variation in EA and RW in termsof two climatic variables: mean temperature and radiation receipt. EA rose linearly with radiation in all three species; increasein EA with temperature was greatest in maize and least (notsignificant) in rape. RWrose with radiation and temperature,the latter being the more important variable especially in coolweather; a temperature optimum was shown at 24° C in rape.FA rose with increase in temperature or decrease in radiation;its variation was due to change in leaf area/leaf weight ratherthan in leaf weight/plant weight. Multiple regression analyses can lead to faulty interpretationif the independent variables are correlated (as are climaticvariables in nature), but conclusions can be checked by controlled-environmentstudies in which climatic factors are not correlated. The presentconclusions are supported by such studies. The regression equations, coupled with average weather records,indicate seasonal cycles of growth parameters. EA is maximalnear midsummer and minimal near midwinter, following the radiationcycle. Maxima and minima in RW are about a month later, becauseRW is affected by the temperature cycle and this lags behindthe radiation cycle. FA is maximal in autumn and minimal inspring. EA is highest where radiation receipts near 750 cal cm2day1 coincide with high temperatures. This combinationoccurs only in clear midsummer weather at low latitudes, andis maintained over long periods only in arid regions. The fact that EA rose linearly with radiation suggests thatleaf water deficits arising under high radiation had littleeffect on EA and that saturating levels of light were very high. 相似文献
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SUSAN E. EVANS FLS LUIS JAVIER BARBADILLO 《Zoological Journal of the Linnean Society》1998,124(3):235-265
The Early Cretaceous (Barremian) lepidosaurian assemblage of Las Hoyas (Cuenca Province, Castilla-La Mancha), Spain, resembles that of roughly contemporaneous localities at Montsec (Catalonia), Una (Castilla-La Mancha) and Galve (Aragon) in being dominated by the scincomorph lizard Meyasaums ( Ilerdaesaurus ). It differs in the presence of two previously unknown taxa, one of which, described here, shows a strikingly unusual morphology in its ribs and distal limb skeleton suggestive of climbing specialization. This form is sufficiently distinct from other known taxa to warrant the erection of a new genus and species, Scandensia ciervensis gen. et sp. nov. Cladistic analysis of Scandensia suggests that it forms a sister taxon to living squamates (Iguania + Scleroglossa and all descendants of their most recent common ancestor). 相似文献
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PRACHY DIXIT SUDHIR SINGH RAMACHANDRAN VANCHEESWARAN KIRANMAYI PATNALA SUSAN EAPEN 《Plant, cell & environment》2010,33(10):1697-1707
Zinc (Zn) is an essential micronutrient required for growth and development of all organisms. Deficiency of Zn in humans is widespread, affecting 25% of world population and efforts are underway to develop crop plants with high levels of Zn in their edible parts. When strategies for enhancing Zn in crop plants are designed, it is essential to exclude cadmium (Cd), a toxic analogue of Zn. In the present work, a high affinity and high specificity zinc transporter gene (tzn1) from Neurospora crassa was cloned and introduced into Nicotiana tabacum with the objective of enhancing the potential of plants for zinc acquisition. When grown in hydroponic medium spiked with 65Zn, transgenic plants showed enhanced accumulation of Zn (up to 11 times) compared to control plants, which was confirmed further by environmental scanning electron microscopy coupled with Energy Dispersive X‐ray analysis. More importantly, no significant difference in uptake of Cd2+, Fe2+, Ni2+, Cu2+, Mn2+ and Pb2+ between the transgenic and control plants was observed. The present studies have shown that Neurospora crassa tzn1 is a potential candidate gene for developing transgenic plants for improving Zn uptake, without co‐transport of Cd and may have implications in Zn phytofortification and phytoremediation. 相似文献
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We explored whether epidermal pressure regulates cell and organgrowth in leaflets ofPisum sativumvar.argenteum,a mutant cultivarof the garden pea characterized by reduced adhesion betweenthe epidermis and subjacent mesophyll. Developing leaflets ofleaves arising at three positions on the seedling axis werepeeledin situand grown to maturity in humidity chambers. Themature anatomy and morphology could be accurately assessed becausewound responses normally associated with peeling were preventedby theArgmutation that permitted peeling without damage to themesophyll and by the humidity chambers that protected peeledareas from desiccation. The mesophyll cell size, state of differentiation,and layering pattern as well as the overall morphology of mature,peeled leaflets were indistinguishable from those of mature,intact leaflets grown under the same conditions. The epidermisexerted no detectable regulatory effect on the expansion ofthe leaflets as a whole or on the tissue layers and cells withinthe leaflets.Copyright 1999 Annals of Botany Company. Biomechanics, compression, epidermis, leaf development, mesophyll, pressure, wound response,Pisum sativumvar.argenteum. 相似文献