During the late nineteenth and early twentieth centuries many studies were made of fertilization in algae (2-4, 8, 9, 13, 16) . Relatively few investigations have been presented that deal with the details of such a phenomenon at the fine structural level . Among those researches which have concerned themselves with gamete union (2, 3, 8), only one (2) has presented any details of pronuclear fusion . It is the purpose of the present paper to relate some fine-structural details of pronuclear fusion in a coenocytic marine green alga, Bryopsis hypnoides . MATERIALS AND METHODSBryopsis hypnoides Lamouroux was collected in the vicinity of Woods Hole, Mass ., during the months of 606 B R I E F N O T E S June, July, August, and September, and placed in culture dishes . Usually within 48 hr of collection, gametogenesis had commenced and the plants could be separated according to sex . Motile gametes, released into sea water in the culture dish, were passed through Whatman #1 filter paper to remove debris .Gametes of both sexes were combined and aliquots were taken at various times up to 65 min after mixing . Two methods of taking samples were used : 1 .) Aliquots were poured into 3% glutaraldehyde in sea water, centrifuged to a pellet, solidified in a drop of agar, and then passed through subsequent steps ; 2 .) Taking advantage of the phototactic response of fusing gametes, the author placed pieces of polymerized Epon in the culture dish near the illuminated side of the dish . The fusing gametes then attached to this surface . The blocks of Epon were then placed in on

Leaves and pith of Turkish, Wisconsin 38, and Samsun NN tobacco (Nicotiana tabacum) varieties, which differ in their sensitivity to tobacco mosaic virus, showed the same qualitative isoperoxidase patterns and a similar distribution of distinctive isoperoxidases between the cell protoplast and wall-free, ionically, and covalently bound fractions. No changes in the qualitative isoenzyme spectrum were found in relation to age, mechanical injury, or leaf infection with tobacco mosaic virus. The distinctive isoperoxidases which reacted to infection were the same as those responsive to mechanical injury, confirming that the enzyme reaction to infection results from a nonspecific response to injury. The increase in peroxidase activity in response to infection or mechanical injury, or both, was greater in young tissue than in the older ones. The great increase in Samsun NN leaves and no increase in those of the two other varieties in response to infection may be due to differences in the degree to which the pathogen affected processes controlling the nonspecific peroxidase reaction to injury. Peroxidase development in the infected Samsun NN leaves was due to isoenzymes which form the wall-bound fraction in very young tissues, and to those which increase in activity with aging in the protoplast and wall-free fractions. In mechanically injured tissue, only the first group of isoenzymes increased in activity. In Samsun NN plants, the increased peroxidase activity in upper intact leaves above the infected ones was only due to isoenzymes whose activity increases with both normal and virus-accelerated senescence. Peroxidase reaction to challenge inoculation in these leaves was the same whether the lower ones were intact, infected and/or mechanically injured. Thus, the induced systemic resistance to tobacco mosaic virus may be due to other than peroxidase factors.In infected tissues, peroxidase was detected in the endoplas. mic reticulum, Golgi apparatus, vacuole, cell wall, and intercellular spaces. The Golgi vesicles were often localized near the tonoplast and plasmalemma, fusing with membranes and secreting their contents. The possible "rejuvenating" effects of injury on synthesis and transport of distinctive isoperoxidases are discussed.eases. Systemic-induced resistance to TMV' in the hypersensitive Samsun NN tobacco plants (9) has been also related to peroxidase; increased peroxidase activity leading to production of toxic compounds causes early killing of infected cells and early formation of a barrier to viral spread (30, 31). Increases in the activity of peroxidase in infected organs, usually referred to the soluble fraction of this enzyme, are assumed by many to result from a nonspecific host response (2,11,18,27,32,34), although new soluble isoperoxidases are claimed to appear in some infected tissues (2,8,10,11,26).Previous study on Wisconsin 38 tobacco plant pith has shown a great increase of peroxidase activity, not only in its protoplast fraction, but also in the wall-bound fraction in response to cuttin...

Leaves and storage roots of sweet potato plants (Ipomea batatas) showed the same qualitative isoperoxidase patterns and a similar distribution of distinctive isoperoxidases between the cell protoplast and cell wall free, ionically bound, and covalently bound fractions. No changes in the qualitative isoenzyme spectrum were found in relation to age, mechanical injury, or ethylene action. Thus, as in tobacco plants, the cell isoperoxidases in sweet potato did not reflect the possible differential mRNA synthesis in relation to organ, age, or injury. Transcription does not seem to be a limiting factor in injury-and ethylene-dependent peroxidase enhancement during the first 24 hr.The contribution of the wall ionically bound and protoplast fractions was highest in young and old leaves, respectively. In the protoplast and wall ionically and covalently bound fractions, 14, 6, and 5 isoenzyme bands were found; in addition, 4 bands, not detected in the protoplast, were also revealed in the covalently bound fraction. The distinctive "juvenile" and, developing with age, "mature" isoforms were mainly found in the ionically bound and protoplast fractions, respectively.The injury-enhanced and/or ethylene-enhanced peroxidase development was most pronounced in young leaves. Ethylene suppressed some injury-enhanced, had no effect on some other injury-enhanced, and greatly promoted some of the injury-unaffected or enhanced isoperoxidases. After ethylene removal, an increase in the "mature" isoforms was found in the protoplast of intact leaves.Electron microscopy of leaves revealed peroxidase in membrane-bound vesicles located mainly in the vacuole; a thin layer of reaction products was also found on the wall's outer surface. No Golgi apparatus were seen in the ceUs of control or ethylene-treated intact leaves. In ethylenetreated intact or injured leaves accumulations of reaction products between the plasmalemma and wall were also found. Numerous Golgi apparatus with dark stained vesicles were seen in injured, and especially in injured and ethylene-treated leaves; the vacuolar bodies seemed to occur in very great number.Previous investigation (2-4) has shown that sweet potato storage roots differ significantly from tobacco pith and leaves and carrot roots in the peroxidase reaction to mechanical injury, C2H4, IAA, and actinomycin D. However, like tobacco tissues, sweet potato root isoperoxidases were distinctive in their distribution between cell wall and protoplast fractions as well as in their reaction to cut injury. The root isoperoxidases were also distinctive in their reaction to C2H4. This report deals mainly with age-, mechanical injury-, and C2H4-related changes in cell peroxidase of sweet potato leaves. MATERIALS AND METHODSHealthy storage roots of Ipomea batatas were purchased locally. Plants grown from several buds of single roots, with 2 to 3 or 7 to 8 shoots, were used in each experiment, especially in experiments in which leaf isoperoxidases were compared to the root isoenzymes.Mechanical injury was induced i...