The net photosynthetic rate of attached primary bean leaves treated with benzyladenine (BA) decreased from 35 nano‐grams carbon dioxide per square centimetre and second (ng cm−2 s−1) at week 2 to 17 ng cm−2 s−1 at week 4, and thereafter increased to 24 at week 6. By contrast the net photo‐synthetic rate of the water‐treated leaves decreased to 4–5 ng cm−2 s−1 at weeks 5 and 6. The stomatal resistance was not markedly affected by BA treatment. The BA‐treated primary leaves had higher dry and specific weights, and the chlorophyll and carotenoid contents were greater than for the water controls. The pigment content of the BA‐treated leaves steadily increased from week 2 to 6, whereas in the water controls it remained constant till week 4 and thereafter decreased. It is concluded that retardation of leaf senescence by BA is assoclatcd with a mnintenance of photosynthetic activity.

The effects of two relative humidities and three temperature regimes on the growth and yield responses of four pea cultivars were investigated. The high day/night temperature regime of 27/17 C, compared with 17/7 C, decreased the number of pods per plant by 46, 65, 66 and 54% in the cultivars Dark Skin Perfection, Nugget, Early Sweet 11 and Elf, respectively. Continued growth at the high temperature decreased pea yield by 50% in Dark Skin Perfection and about 70% in the other cultivars. When plants were first grown at 17/7 until full bloom and then subjected to the 27/7 C regime, the high temperature treatment showed no significant effect on growth and yield. Dark Skin Perfection was the least adversely affected by high temperature. No significant differences in growth and yield were observed at 50 and 90% relative humidities.

Abscisic acid treatment of primary bean leaves caused a partial closure of stomates and thus considerably reduced the phytotoxicity of ozone. The symptoms of ozone-induced phytotoxicity in the water-treated leaves are a marked decrease in chlorophyll and slight decreases in the levels of protein and RNA. The evidence indicates that ozone injury to leaves is not metabolically related to normal leaf senescence.

Ozone effects on growth of radish plants as influenced by nitrogen and phosphorus nutrition and by temperatureSummary Raphanus sativus L. (radish) plants were grown in sand culture at two temperatures and fed with nutrient solutions containing relatively low or high levels of either N or P. At the 4-leaf stage, the plants were exposed to ozone at a concentration of 25 pphm for 4 h. Ozone treatments resulted in decreased dry weight of low-and high-N plants at both temperatures and of low and high P plants only at the lower temperature. The study showed that air pollutant growth reduction is not necessarily accentuated by luxuriant growth resulting from high nutritional status. Responses to the nutrition of specific mineral nutrients depend on the modifying effect of temperature.

Tomato (Lycofiersicon esculewtum Mill.) plants were grown in controlled environments and subjected to different soil water regimes. At 3-, 5-, and 7-leaf growth stages, plants were fumigated with ozone at 50 or 100 pphm for 1 h.Plants at 5-or 7-leaf stage were not as sensitive to ozone as were the young plants fumigated at 3-leaf stage. At the 7-leaf stage, leaf injury at nearoptimum water condition was very minimal, even at ozone concentration of 100 pphm.Ok&e treatment decreased total dry matter of optimally watered plants fumigated at the 3-leaf stage. Plants subjected to water stress resulting in low ieaf relative turgidity-prior to ozoie fumigation, were considerably protected from ozone phytotoxicity.Open stomata were an important factor in ozone phytotoxicity.Post-fumigation water regimes had no effect on eventual leaf injury.