Search

Two distinct morphological forms characterize the ontogeny of many epiphytic bromeliads. Smaller plants exhibit an atmospheric habit, while larger plants form water-impounding tanks. The study of the functional significance of heteroblasty in epiphytes is severely hampered by considerable size-related variation in morphological, anatomical and physiological parameters. To overcome this problem, plants of varying size of both atmospheric and tank form were included in the present study withVriesea sanguinolenta. The results show that virtually all morphological, anatomical and physiological characteristics vary during ontogeny, but changes were rarely directly related to the step change in gross morphology. Changes were either: (1) gradual from smallest atmospheric to small tank (e.g. leaf divergence angles, reduction in photosystem II efficiency during drought, speed of recovery after drought); (2) there was no change between atmospheric and small tank, but a gradual or step changewithinthe tank form (stomatal density, relationship of leaf N and specific leaf area); or (3) developmental patterns were more complicated with decreases and increases during ontogeny (photosynthetic capacity, carbon isotope ratios, abscisic acid levels during drought). Although the comparisonsbetweenontogenetic phases were always confounded by size differences, a hypothetical small tank plant is expected to suffer higher water loss than a real atmospheric, whereas a hypothetical, large atmospheric plant would show reduced access to resources, such as nutrients, in comparison with the real tank. The present results are consistent with the notion of heteroblasty as an adaptation of early ontogenetic stages to drought, but highlight that size-related variation greatly modifies any difference directly associated with the step change from atmospheric to tank. [ABSTRACT FROM AUTHOR]

Focuses on the effect of mechanical milling on free volume. Use of gel permeation chromatography measurements; Impact of long-time milling with free volume; Heat treatment above the glass transition temperature dominate.

The occurrence of crassulacean acid metabolism (CAM) among the epiphyte flora of the lowland forest on Barro Colorado Island (BCI), Panama, was investigated. A total of 116 species was included, i.e. about 2/3 of the known epiphyte taxa. As judged from the carbon isotope ratios and the absence of Kranz anatomy, indications of CAM were found in 29 species of three families, Orchidaceae (20), Bromeliaceae (7), and Cactaceae (2). We estimate that about 25% of the epiphyte flora of BCI are CAM plants. Cam was most prevalent in exposed sites, but even in the understorey two epiphyte species engage in CAM. [ABSTRACT FROM AUTHOR]

The penetration of 137Cs by contact exchange through cuticular membranes from the adaxial surface of leaves of Pyrus communis and Prunus cerasus has been investigated. The resistance of the cuticles to the caesium penetration was dependent on the counterions associated with the fixed negative ion exchange sites in the membranes The mobility of hydrated potassium ions and their tenuous connection to -COOH--groups in the membrane encouraged caesium permeation in contrast to cuticular membranes with predominatly protonized ion exchange sites. Divalent calcium ions caused a strong reduction (4-20 times) of the caesium permeability which is decisive for the calculation of the caesium uptake by the intact leaf. Under these conditions, a penetration rate of the deposited caesium of 0.11 ±0.05% h-1 for pear cuticles and of 0.036±0.025% h-1 for cherry cuticles was measured after the adjustment to steady state conditions. Approximately 12-24% and 4.5-7.5% of initially retained caesium could be absorbed by the leaves of pear and cherry, respectively, in a rain free-period of 7 d in the area of Munich after wet deposition of fallout from the Chernobyl reactor accident. Furthermore, the caesium penetration from the physiological inside to the outside of the membrane was found to be smaller by a factor of 100-150 compared with that of the opposite directions [ABSTRACT FROM AUTHOR]

Irradiation of fully developed green leaves as well as irradiation of isolated chloroplasts causes a rapid, reversible increase in the activity of NADP-linked phosphoglyceraldehyde dehydrogenase. This increase is closely connected with the functioning of the non-cyclic electron flow of photosynthesis. It is accompanied by a decrease in the activity of the NAD-linked enzyme. The experiments presented here show that it is not the kinase but the dehydrogenase which is the rate limiting factor in the over-all reaction measured up to date. The activation of the ‘dark-enzyme’ (= basic enzyme) resulting in the ‘light-enzyme’ (= activated enzyme) is not due to an unspecific reduction of S-S-groups in the reactive center. Dithiothreitol only restores the activity lost during the isolation procedure of the chloroplasts. NADPH rather than dithiothreitol causes a specific activation of the basic enzyme. How- ever the basic enzyme must be present in the completely reduced form to undergo maximal activation. Incubation with dithiothreitol and NADPH thus results in an activation rate as high as that caused by light in vivo. Activation of the NADP-linked dehydrogenase could also be attained by NADPH after its partial purification by ammonium sulfate fractionation. The activation rate by incubation with different concentrations of NADPH shows a sigmoidal type of curve. There are characteristic differences in sensitivity between the activity of the basic enzyme and its ability to be activated at different temperatures between 52°–60°. The results indicate that the action of NADPH may be an anosteric one, causing a transition from a NAD- (or possibly a NAD + NADP)-dependent to a NADP-dependent form of the enzyme. A diagram for a feed-forward activation of the NADP-linked dehydrogenase which possibly takes part in regulation of C02-fixation is presented. [ABSTRACT FROM AUTHOR]