Photosynthetic performance of vegetative and reproductive structures of green hellebore (Helleborus viridis L. agg.)

Abstract

Photosynthetic irradiance response of vegetative and reproductive structures of the green-flowered deciduous perennial green hellebore was studied by the comparative use of chlorophyll (Chl) fluorescence techniques and gas exchange measurements. All the Chl-containing organs (leaves, sepals, stalks, and fruits) examined were photosynthetically active showing high intrinsic efficiencies of photosystem 2 (F v /F m : 0.75-0.79) after dark adaptation. Even in the smaller fertile and sterile parts of the flower (nectaries and anthers) a remarkable photosynthetic competence was detected. With increasing photon flux densities (PFD) electron transport rates, actual quantum yields, and photochemical quenching coefficients of the main photosynthetic organs decreased in the order: leaf>sepal>fruit>stalk. At moderate to high PFDs the sepals achieved maximum electron transport rates corresponding to about 80 % of concomitant mature leaves. In contrast, maximum net photosynthetic rate of the sepals [2.3 µmol(CO 2 ) m -2 s -1 ] were less than one fourth of the leaves [10.6 µmol(CO 2 ) m -2 s -1 ]. This difference is explained by a 70-80 % lower stomatal density of sepals in comparison to leaves. As the basal leaves emerge late during fruit development, the photosynthetically active sepals are a major source of assimilates, contributing more than 60 % of whole-plant CO 2 gain in early spring. The ripening dehiscent fruits are characterized by an effective internal re-fixation of the respirational carbon loss and thus additionally improve the overall carbon budget.

Using remotely sensed spectral reflectance to indicate leaf photosynthetic efficiency derived from active fluorescence measurements

“…In experiment I, F v ∕F m values of fresh leaves ranged mostly from 0.75 to 0.85 [ Fig. 1(a)], which were similar with observations by Aschan et al, 58 that this ratio differed insignificantly in unstressed plants. In experiment II, however, F v ∕F m could drop below 0.5 after 7 h of leaf removal while leaf chlorophyll content varied only slightly within a day (SPAD value almost the same).…”

Important photosynthetic contribution from the non-foliar green organs in cotton at the late growth stage

“…Based on the mean surface area and the O 2 evolution rate of each Chlcontaining organ during the growth stages (Figs. 1, 2), the relative photosynthetic contribution of the different parts to the total plant in terms of carbon assimilation was estimated by multiplying the O 2 evolution rate per area by the total area of the respective organ (Table 2), following the method of Aschan et al (2005) who used the CO 2 exchange rate. As shown in Table 2, the photosynthetic contribution of stalks and the bolls (bracts plus capsule wall) were 9.7 and 4.4% of the total, respectively, at the peak flowering stage.…”

“…The photosynthetic performance of the non-foliar organs is more and more studied by the chlorophyll (Chl) fluorescence techniques Pfanz 2003, 2006;Aschan et al 2005). However, chlorophyll fluorescence data do not necessarily represent the photosynthetic status of the whole leaf tissue, especially in thick leaves, a deficiency which has been shown by close comparisons of the electron transport rates measured with chlorophyll fluorescence and with gasexchange (Kingston-Smith et al 1997;Tsuyama et al 2003).…”

Reproductive Development of the Christmas Rose (Helleborus niger L.): The Role of Plant Hormones

“…27 Comparable, green sepals of Helleborus viridis contribute more than 60 % of the whole-plant CO 2 gain in early spring. 33 Young inflorescences of the terrestrial orchid Spiranthes cernum achieved one-third of the leaf photosynthesis. 34 Green spots on the white inner tepals of Snowdrop (Galanthus nivalis L.), 35 and white perigon tips of Leucojum vernum L. 36 achieved photosynthesis of about one-forth and one-third of that measured in the fully developed leaves, respectively.…”