Ombrohydrochory in Thismia panamensis (Standley) Jonk: a mycoheterotrophic species in Brazilian Cerrado forests.

Species of the genus Thismia Griff. are small herbs, considered mycoheterotrophic due to an intimate relationship with fungi. They are achlorophyllous, with complex floral structure but little information on reproductive strategies. This study evaluated structural and ecological aspects associated with the dispersal of seeds of Thismia panamensis (Standley) Jonk. The study was carried out in a forest fragment in the Brazilian Cerrado. During the reproductive period, 36 individuals were monitored for spatial distribution of the population and their fruits were collected. Samples were subjected to light microscopy and microtomography techniques, in addition to an experiment to evaluate seed dispersal by water droplets. Thismia panamensis is up to 8-cm tall, with a tuberous root and stem, without leaves. Its fruit is dehiscent, cup-shaped, 5 ± 1 mm in diameter, containing 219.33 ± 106.70 seeds, with an average length of 0.55 ± 0.07 mm. The seeds are exposed, and their coat has a thin and lignified wall. Accumulation of secretions was observed inside the fruits. The innermost cell layer of the ovary showed typical characteristics of aquiferous parenchyma. Water splash experiments showed that the seeds reached an average distance of 44.04 ± 26.58 cm. Each splash contained, on average, 1.50 ± 1.23 seeds, with 75% of the splashes containing a single seed. A total of 239 seeds were counted in the 163 splashes evaluated. The data show potential seed dispersal by ombrohydrochory in T. panamensis, favouring its maintenance in the study area and reflecting its clumped spatial distribution.

Albinism in plants - far beyond the loss of chlorophyll: Structural and physiological aspects of wild-type and albino royal poinciana (Delonix regia) seedlings.

The partial or complete loss of chlorophylls, or albinism, is a rare phenomenon in plants. In the present study, we provide the first report of the occurrence in albino Delonix regia seedlings and describe the morpho-physiological changes associated with albinism. Wild-type (WT) and albino seedlings were characterized. Leaflets samples were processed following common procedures for analysis with light, scanning and transmission electron microscopy. The chlorophyll a fluorescence parameters and the carbohydrate, lipid and soluble protein content were also determined in leaf and cotyledon samples of both albino and WT seedlings. Albino seedlings showed reduced growth. They also had lower chlorophyll and protein content in foliar tissues than WT seedlings, in addition to lower concentrations of lipids and carbohydrates stored in cotyledons. The chloroplasts of albino seedlings were poorly developed, with an undefined internal membrane system and the presence of plastoglobules. Wild-type seedlings had a uniseriate and hypoestomatic epidermis. The mesophyll was dorsiventral, consisting of a layer of palisade parenchyma and two to four layers of spongy parenchyma. In albino seedlings, the spongy parenchyma was compact, with few intercellular spaces, and the thickness of the mesophyll was larger, resulting in increased thickness of the leaf blade. Albino seedlings had higher stomatal density and number of pavement cells, although the stomata had smaller dimensions. In addition to the partial loss of chlorophylls, albino D. regia showed changes at physiological and structural levels, demonstrating the crucial nature of photosynthetic pigments during the development and differentiation of plant leaf tissues/cells.

Auxin and physical constraint exerted by the perianth promote androgynophore bending in Passiflora mucronata L. (Passifloraceae).

The androgynophore column, a distinctive floral feature in passion flowers, is strongly crooked or bent in many Passiflora species pollinated by bats. This is a floral feature that facilitates the adaptation to bat pollination. Crooking or bending of plant organs are generally caused by environmental stimulus (e.g. mechanical barriers) and might involve the differential distribution of auxin. Our aim was to study the role of the perianth organs and the effect of auxin in bending of the androgynophore of the bat-pollinated species Passiflora mucronata. Morpho-anatomical characterisation of the androgynophore, including measurements of curvature angles and cell sizes both at the dorsal (convex) and ventral (concave) sides of the androgynophore, was performed on control flowers, flowers from which perianth organs were partially removed and flowers treated either with auxin (2,4-dichlorophenoxyacetic acid; 2,4-D) or with an inhibitor of auxin polar transport (naphthylphthalamic acid; NPA). Asymmetric growth of the androgynophore column, leading to bending, occurs at a late stage of flower development. Removing the physical constraint exerted by perianth organs or treatment with NPA significantly reduced androgynophore bending. Additionally, the androgynophores of plants treated with 2,4-D were more curved when compared to controls. There was a larger cellular expansion at the dorsal side of the androgynophores of plants treated with 2,4-D and in both sides of the androgynophores of plants treated with NPA. This study suggests that the physical constraint exerted by perianth and auxin redistribution promotes androgynophore bending in P. mucronata and might be related to the evolution of chiropterophily in the genus Passiflora.