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 dark-forced 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 2-week-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 (cotyledon vs. leaves) also strongly influenced the essential oil composition. Therefore, light conditions and developmental stage are both important factors to be considered in case of potential therapeutic, culinary or aromatic uses of rosemary leaves and their essential oils.

Protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in epicotyls of 14-day-old dark-germinated seedlings and in 100-day-old dark-grown stems of red oak (Quercus rubra L.). Fluorescence spectroscopy measurements of epicotyls at 77 K showed that the majority of Pchlide and Pchl is present as a shorter wavelength-emitting monomer with a fluorescence emission maximum at 629–631 nm. A small amount of a monomeric form emitting at 635–636 nm was also present. Minor amounts of Pchlide were aggregated into larger complexes with fluorescence emission maxima at 640, 644–646 and 652–654 nm, as seen in etiolated leaves. Flash illumination transformed the 652–654-nm-emitting form to chlorophyllide, but not those forms with emission maxima at 629–631, 635–636 and 644–646 nm. These shorter wavelength-emitting forms were transformed to chlorophyllide by continuous illumination, but the process took several hours. Epicotyls and young stems were light sensitive, with exposure to full daylight causing strong pigment bleaching and tissue destruction. Complete greening took place only at low irradiances. Light sensitivity was greater at 4 °C than at room temperature. We conclude that the monomeric arrangement of the pigments accounted for the light and temperature sensitivity of the greening process in epicotyls and stems.

Drought is one of the major abiotic stresses that frequently causes severe loss in crop yield worldwide. Laboratory predictors of field drought tolerance could significantly increase the effectiveness of existing plant breeding programs. In earlier field experiments, drought tolerance of 22 cultivated barley varieties has already been quantified. In order to develop laboratory markers of drought sensitivity, field drought tolerance data were correlated with parameters obtained in laboratory tests. Root and shoot length and weight were measured on control and PEG-treated (a simple laboratory drought model) seedlings. Significant correlations were found among root growth, shoot weight in laboratory stress conditions and field drought tolerance. Interestingly, a negative correlation was found between root length of the untreated seedlings and drought tolerance. Laboratory Drought Tolerance Index (DTI) was introduced as the linear combination of those laboratory parameters which were correlated with field drought tolerance. DTI showed good predictive value (r = 0.57, p < 0.05) for drought tolerance in field experiments and we suggest it for preselection of drought tolerant barley breeding lines and for the characterization of drought tolerance in general.

Bud scales (cataphylls) protect latent shoot apices and preformed organs in the majority of deciduous trees, yet these modified structures of leaf origin and their potential other functions are rarely studied in detail. Here, we investigated seasonal and developmental variations in anatomy by bright-field microscopy; plastid ultrastructure by transmission electron microscopy; optical properties, photosynthetic pigment contents and organization by various spectroscopic methods; photosystem II (PSII) activity by Imaging PAM; and gross photosynthesis by infrared gas exchange analysis in outer brownish and inner greenish bud scales of horse chestnut (Aesculus hippocastanum L.) throughout their lifespan, i.e. from their initiation end of spring until their senescence after the bud break next year. The composition of the resin secreted on the outer bud scales was characterized by HPLC-UV-HRMS following acetonic extraction, revealing methoxylated flavonols as the dominant constituents and suggesting additional roles in photoprotection and chemical defense. Both outer and inner bud scales retained structurally intact, photosynthetically competent chloroplasts throughout all seasons, despite low chlorophyll content and limited photosynthetic capacity. Outer scales exhibited strong light-filtering, photoprotective properties, and pronounced seasonal downregulation of photosynthetic performance, besides their known roles in thermal insulation, and environmental shielding. In contrast, inner scales maintained higher chlorophyll content, more stable PSII efficiency during dormancy, and rapidly recovered photosynthetic activity during bud break, indicating a metabolically poised state supporting early spring development. Our findings underscore bud scales' multifunctional roles as protective barriers and active contributors to plant physiology by photosynthesis and the maintenance of chloroplast ultrastructure throughout their lifespan.