Promjene kloroplasta u listovima kupine tijekom vegetacijske sezone

The ultrastructure, pigment content and photosynthetic activity of chloroplasts in blackberry (Rubus fruticosus L. s. 1.) leaves were investigated during spring, summer, autumn and winter. The fine structure of young spring leaves shows all characteristics of the young leaf tissue with the maximum value of photosynthetic activity. Their ultrastructure changes parallelly with the development and maturation of these leaves through summer and autumn. Chloroplasts of the summer leaves have a well developed thylakoid system with big grana, and starch is always present in the stroma. The content of pigments reaches its maximum in the summer leaves but the photosynthetic activity slowly falls. A reduction in the thylakoid system and enlargement of plastoglobules are the features of chloroplasts in the autumn leaves. Their photosynthetic activity and content of pigments are low, so these leaves gradually decay. New leaves which grow up in the late summer and early autumn, remain on the shrubs throughout winter, and end their lifespan in the late spring. Chloroplasts of the winter leaves have a well developed thylakoid system and numerous plastoglobules in the abundant stroma. It is significant that these leaves are exposed to low temperatures and short days throughout the period from autumn to winter and thus they are adapted to low temperatures. The winter leaves have large chloroplasts and a high content of pigments, but their photosynthetic activity is relatively low. The fine structure of the winter leaves frozen to subzero temperatures (up to —12°C), was also examined. Cells of these leaves have a dense cytoplasm pushed among cell organelles, many small vacuoles and numerous vesicles.Istražene su promjene u ultrastrukturi, sadržaju pigmenata i foto- sintetskoj aktivnosti u kloroplastima listova kupine (Rubus fruticosus L. s. 1.) tijekom proljeća, ljeta, jeseni i zime. Ultrastruktura mladih proljetnih listova pokazuje karakteristike mladog lisnog tkiva uz maksimalne vrijednosti fotosintetske aktivnosti. Tijekom ljeta i jeseni, usporedo s razvojem i starenjem tih listova, njihova ultrastruktura se mijenja. Kloroplasti ljetnih listova imaju dobro razvijen tilakoidni sustav i velika grana, a zrnca škroba redovito su prisutna. Sadržaj pigmenata tada dosiže maksimum, dok fotosintetska aktivnost postupno opada. Redukcija tilakoidnog sustava te povećanje broja i veličine plastoglobula obilježja su kloroplasta starih jesenjih listova. Njihova je fotosintetska aktivnost niska kao i sadržaj pigmenata i takvi listovi postupno propadaju. No, krajem ljeta i početkom jeseni izrastaju novi listovi koji se zadržavaju preko zime i propadaju tek u kasno proljeće. Kloroplasti zimskih listova imaju dobro razvijen tilakoidni sustav i malobrojna ali velika grana te obilnu stromu s dosta plastoglobula. Značajno je da su ti listovi tijekom jeseni i zime izloženi postupnom padu temperature i promjeni fotoperiode što uzrokuje njihovo prilagođavanje na niske temperature. Zimski listovi imaju velike kloroplaste i visok sadržaj pigmenata, no njihova fotosintetska aktivnost je relativno niska. Istražena je i ultrastruktura smrznutih zimskih listova na temperaturama ispod 0 °C (do —12 °C). U stanicama tih listova redovito nalazimo više manjih vakuola i brojne vezikule, a gusta citoplazma potisnuta je između staničnih organela