It is unclear whether light affects the structure and activity of exogenous secretory tissues like glandular hairs. Therefore, transmission electron microscopy was first used to study plastid differentiation in glandular hairs and leaves of light-grown rosemary (Rosmarinus officinalis "Arp") plants kept for 2 weeks under ambient light conditions. During our detailed analyses, among others, we found leucoplasts with tubuloreticular membrane structures resembling prolamellar bodies in stalk cell plastids of peltate glandular hairs. To study the effect of darkness on plastid differentiation, we then dark-forced adult, light-grown rosemary plants for 2 weeks and observed occasionally the development of new shoots with elongated internodes and pale leaves on them. Absorption and fluorescence spectroscopic analyses of the chlorophyllous pigment contents, the native arrangement of the pigment-protein complexes and photosynthetic activity confirmed that the first and second pairs of leaf primordia of darkforced shoots were partially etiolated (contained low amounts of protochlorophyll/ide and residual chlorophylls, had etio-chloroplasts with prolamellar bodies and low grana, and impaired photosynthesis). Darkness did not influence plastid structure in fifth leaves or secretory tissues (except for head cells of peltate glandular hairs in which rarely tubuloreticular membranes appeared). The mesophyll cells of cotyledons of 2week-old dark-germinated rosemary seedlings contained etioplasts with highly regular prolamellar bodies similar to those in mesophyll etio-chloroplasts of leaves and clearly differing from tubuloreticular membranes of secretory cells. Analyses of the essential oil composition obtained after solid phase microextraction and gas chromatography-mass spectroscopy showed that in addition to light, the age of the studied organ (i.e., first leaf primordia and leaf tip vs. fifth, fully developed green leaves) and the type of the organ

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by(14)CO2 fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.

The photosynthetic activities of barley leaves in vivo and of thylakoids, isolated from the leaves, in vitro were studied during greening in the presence or absence of 2 × 10-4 м SAN 6706. The degree of chlorophyll bleaching increased from 32% at 24 h of greening to 60% at the final stage. Treated leaves were unable to carry out 14CO2-fixation, their fluorescence induction properties showed very limited, if any, photosystem II-activity, and the thylakoids isolated from the leaves were also inactive in mediating ferricyanide Hill reaction. The leaves, however, exhibited lightinduced quenching of fluorescence revealed by slow fluorescence induction measurements; and the thylakoids were active in mediating photosystem I-specific in vitro Mehler reaction. Thylakoid membranes of the chloroplasts isolated from treated leaves contained CP 1 and LHCP3 bands as revealed by polyacrylamide gel electrophoresis. From these results it is concluded that i) greening in the presence of SAN 6706 leads to the formation of inactive photosystem -II units; that ii) photosystem-I per se is active in vitro, and can, possibly, mediate cyclic electron transport in vivo coupled to the formation of ATP; and that iii) the presence of xanthophyll pigments is required for the assembly of the light-harvesting complex.The experiments were repeated with the application of SAN 9789, another pyridazinone compound, and yielded practically the same results as those obtained with SAN 6706. For practical reasons, only the results obtained with SAN 6706 are demonstrated throughout this communication.

Köszönetnyilvánítás: Ezt a kutatást az Emberi Erőforrások Minisztériuma támogatta az ÚNKP-17-4-III-ELTE-128 projekt keretében (S.K.).