The role of copper in photosynthetic organisms depends greatly on its concentration. Copper, as cupric ion, in trace amounts is an essential micronutrient for algae and higher plants (17,20) and is an essential constituent of several enzymes such as polyphenol oxidase (3) and plastocyanin (8), a component of photosynthetic electron transport. Concentrations higher than 1 /tm are increasingly toxic to algal and higher plant tissues (4, 13). Cupric sulfate has been extensively used as an algaecide since the beginning of the century (12). The cupric ion has been shown to be an inhibitor of photosynthesis in algal cells (4,11,16) and to inhibit photosynthetic electron transport in isolated chloroplasts (5, 10).The mechanism by which the Cu'+ inhibits the photosynthetic apparatus has been only partially elucidated thus far. The data on inhibition of photosynthesis in isolated chloroplasts gives an incomplete picture of the specific sites of inhibition in the electron transport chain. Macdowall (10) He studied the effect of light intensity on inhibition and concluded that the light reactions were directly affected by Cu21. In addition, Haberman (5) using chloroplasts from Phytolacca americanca showed that both the Hill and Mehler reactions were inhibited by Cu2+ but that the Mehler reaction was inhibited by lower concentrations of the ion.In contrast to Macdowall, Haberman concluded that Cu2+ was inhibiting a dark reaction and did not alter the reactions associated with the photoacts. She observed that Mn2+ added at a concentration of 0.5 mm reduced the inhibition of chloroplasts by Cu2+ and postulated that the Cu2+ was affecting the site of manganese function in 02 evolution. Recently exogenous Mn2+ has been shown to donate electrons after the water oxidation site of photosystem II of isolated chloroplasts (2), suggesting that, at high concentrations, manganese functions in a way other than its primary role in the water oxidation act.This work was conducted with the purpose of resolving the sites of Cu2+ inhibition in photosynthetic electron transport. Since previous work and our preliminary experiments pointed to the fact that photosystem II is preferentially inhibited by Cu2+ emphasis was given to finding the specific sites of inhibition within this photosystem. MATERIALS AND METHODSChloroplasts were prepared from market-grown spinach (Spinacia olercacea L.) as described by Robinson and Stocking (14). MnCl2 was excluded from the grinding and resuspending media in the preparations where Mn2+ was used as an electron donor. Chlorophyll was determined by the method of Arnon (1). Ferredoxin was isolated by the method of San Pietro (15) as modified by Swader and Jacobson (18). The 02 evolving capacity of the chloroplasts was destroyed by a mild heat treatment as described by Hinkson and Vernon (6). The chloroplasts were uncoupled by adding ammonium ions following the principle discovered by Krogman et al. (9).The normal reaction media for studying 02 evolution had the following composition in a total volume of 2...

Autotrophic growth, photosynthesis, and respiration ofChlorella sorokinianaShihira and Krauss were inhibited by the cupric ion, but photosynthesis was more sensitive than respiration. The percent inhibition was determined by the ratio of cells to cupric ions present. Photosynthesis and respiration were inhibited within 2 and 5 min, respectively, after adding 1.0 mM cupric ions.Chlorellacells which had been incubated for a short time in concentrations of the cupric ion that completely inhibited photosynthesis were not able to grow when cultured in a fresh medium without cupric ions, indicating high concentrations of the ion may have destroyed the photosynthetic apparatus and deprived the cells of their ability for autotrophic growth. Dark preincubation of the cells, as well as high bicarbonate concentrations in the assay medium, decreased inhibition. Treatment with cupric ions reduced the cellular chlorophyll and sulfhydryl content, but anaerobiosis, a condition that increased toxicity, had little effect on the sulfhydryl content. Electron transport in photosystems I and II in intactChlorellacells was inhibited, but the specific sites of inhibition in the photosynthetic electron transport chain could not be determined using intact cells.

Studies were conducted to determine the effect of scion-rootstock combinations on premature fruit drop. Ten-year-old trees of the varieties Parvin and Tommy Atkins grafted on Eldon, Malda, Colombo Kidney, Julie, and Cuban were used. The number of prematurely dropped fruits was counted weekly for eight consecutive weeks after flowering. A smaller fruit drop index was observed when Parvin was grafted on Malda, Julie, and Cuban than when grafted on Colombo Kidney. There was no significant difference in fruit drop index between Eldon and Colombo Kidney. Fruit drop index was greater in Parvin than in Tommy Atkins.

Studies were conducted at the Fortuna Substation for 10 years to determine the effect of 5 interstems on growth and yield components of 2 commercial mango varieties. The interstems did not significantly affect the rootstock diameter when Edward variety was the scion; however, they did with Palmer variety as scion at the 3- and 6-year stages only, Irwin interstem diameter at the 3-year stage for Edward and Palmer, and at the 6- and 9-year stages for Edward, was significantly thicker than that of the other interstems. Edward on Manzano Tetenené had the thinnest interstems. In the two varieties studied, the scion diameter was scarcely affected by the interstems at 3, 6 and 9 years after transplanting. Edward and Palmer grafted on Irwin as interstems had significantly lower scion/interstem ratios. The opposite was true when these varieties were grafted on Julie. Three years after planting, the smallest trees were those of Edward and Palmer grafted on Malda; 6 and 9 years after planting, those of Edward grafted on Malda and Manzano Tetenené. Yield efficiency decreased significantly with tree age and size. Thus, there was a negative correlation between these parameters. Edward produced significantly more fruits than Palmer at the 3-year-old stage. Edward as interstem grafted on Eldon produced significantly more fruits at the 3-, 6- and 9-year stages than when grafted on the other interstems. Palmer grafted on Eldon was significantly more precocious than when grafted on the other interstems. Malda and Manzano Tetenené as interstems significantly reduced tree size of Edward; Julie as interstem reduced the size of Palmer.

Experiments were conducted at Adjuntas substation in the central mountain region of Puerto Rico to determine the effect of four rootstocks on growth and fruit production parameters of six clones of Valencia orange. Concerning fruit characteristics, the most notable differences among clones were in size, but also statistical differences were found in peel percentage and number of seeds per fruit. Significant differences in juice characteristics among clones were also found. Fruit production was superior for all four clones with Cleopatra mandarin as rootstock.There was significant difference between clones 3164 and 3264 concerning fruit production. There were no significant differences in yield efficiency during the first crop year; however, trees on Cleopatra mandarin and sour orange rootstocks were significantly taller, wider and had larger canopy volumes. Significant differences among different clones within particular rootstocks were found for tree height, tree width, canopy volume, fruit production and yield efficiency.