Starch synthesis in leaves was increased by phosphate starvation or by treatments which decreased cytoplasmic orthophosphate levels (such as mannose feeding). Usally less than 30% of the total carbon fixed during CO2 assimlation was incorporated into starch in spinach (Spinacia oleracca L.), spinach beet (Beta vulgaris), and tobacco (Nicotiana tabacum) leaves.In isolated spinach chloroplasts, formation of starch from CO2 was usualy less than in leaves.
When added singly to chloroplasts isolated from young pea (Pisum sativum) leaves, both inorganic pyrophosphate (PPi) and smaO quantities (0.2 mM) of ADP inhibit photosynthesis, but when added together they cause a marked stimulation. ATP (at 0.2 mM) is less inhibitory (or not inhibitory) when added alone, but like ADP, stimulates when added in the presence of PPi. This behavior is in marked contrast to that of spinach (Spinacia oleracea) chloroplasts which are normally stimulated rather than inhibited by PPi and which are largely unresponsive to exogenous adenylates. The inhibitory behavior of PPi with pea chloroplasts was observed under conditions where external hydrolysis to Pi is negligible. It is proposed that the exchange of organic and PPi across the chloroplast envelope may be more rapid in chloroplasts from young pea leaves than in chloroplasts from spinach and that interaction between these two processes could account for the princpal observations. The question of adenylate transport across the chloroplast envelope in C3 plants has been debated for some years. Once it had been established that photophosphorylation could occur at high rates (2), it seemed unlikely that this process would not contribute directly to the energy metabolism of the cell. Nevertheless, it became evident at an early stage (27) that photophosphorylation of exogenous ADP was much more rapid if the limiting envelopes were removed by osmotic shock and that the relatively low rates achieved by "intact" chloroplasts could be ascribed to the inevitable presence of a small percentage of damaged chloroplasts in the same preparation (22). Similarly, the work by Heldt and his colleagues on the adenylate translocator appeared to put the fastest rate of transport via this mechanism at about 5 ,umol -mg-' Chl -hr-' and continuous exchangeat '/lo of this value or less (7). Indeed, Heldt et al. (9) have concluded that the adenine nucleotide translocator "does not participate in the photophosphorylation of cytoplasmic ADP." Nevertheless, there have been reports from time to time which put a contrary view (see 3, 11, 14, 19, 26). The earliest of these prompted Stokes and Walker (20) to devise what they believed might be a definitive experiment. In it they showed that ATP could not restore PGA-dependent 02 evolution in uncoupled chloroplasts with intact envelopes but could bring about such a restoration in a reconstituted chloroplast system in which any barrier to ATP entry had been removed. It was accepted, of course, that this approach would fail to detect ATP import dependent on coupled electron transport but it seemed to pro-' Supported in part by the
In the study of three different aquatic ecosystems connected with the Danube river we determined the concentrations of macronutrients (N, P, K, Ca), Na and heavy metals (Fe, Mn, Ni, Pb and Cd) in the most common submerged, floating and emerged aquatic plants: Ceratophyllum demersum, Myriophyllum spicatum, Va llisneria spiralis, Salvinia natans, Hy drocharis morsus ranae, Trapa longicarpa, Nymphoides flava, Nymphaea alba, and Phragmites communis. Analyses were done during the seasonal biomass peak (June-Au gust) in 1999. Significantly higher macronutrients and heavy metal concentrations in sub merged when compared to floating and emerged aquatic plants were found. From the heavy metal concentrations which were measured, iron showed the highest values followed by manganese, nickel and lead, while cadmium exhibited trace concentrations. The degree of metal accumulation in plant tissues (expressed as tissue metal concentration/surrounding water concentration ratio) was locality-dependent. The highest degree was recorded for Mn and Fe. The obtained results indicated an evident chemical pollution of the DTD canal section (near Novi Sad) where V. spiralis had the highest bioaccumulation of Fe and Mn.
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