Abstract Studies focusing on terminal drought combined with heat impacts on plants of agronomic value remain scarce, and even less under field conditions. The objective of this study was to investigate leaf structural and ultrastructural changes induced by heat stress (HS) and drought stress (DS) during seed filling and their relationship with physiological variables and yield determination. Two soybean cultivars were grown in field conditions. During seed filling four treatments were applied, including a control (without manipulation, at ambient temperature and field capacity), HS (episodes exceeding 32°C for 6 h d-1) during 21-d, DS (20% of field capacity soil water content) during 35-d, and HS×DS. Drought principally reduced leaf area, whereas heat decreased leaf thickness, possible as acclimation strategies, but also irreversible reducing CO2 assimilation sites. Both stresses damaged the outer and inner membranes of chloroplasts, causing swollen chloroplasts and accumulation of plastoglobules, loss of chlorophyll content, and negatively affecting chlorophyll fluorescence. Thus, the performance and integrity of the photosynthetic machinery were reduced. Through a morpho-functional perspective and a holistic multiscale approach, our results provide evidence of photosynthesis impairment and yield drops under stressful conditions which were associated with structural and ultrastructural (particularly at the level of chloroplasts) modifications of leaves.

Abstract Floral nectaries are essential for plant reproduction but little is known about the relationship between these secretory structures and pollination system in cacti. To test phenotypic patterns in nectaries associated with pollination syndromes and/or with its pollinators, we selected from evolutionarily related genera Cleistocactus, Denmoza, and Echinopsis, a set of species with bird-pollinated flowers and floral traits that may fit with ornithophily or with sphingophily, and other set of sphingophilous species with moths as effective pollinator. Observations were made under light microscope and scanning and transmission electron microscopes. Nectaries are located at the base of the filaments welded to the tube, forming a chamber. The nectary consists of the epidermis with distinctive features in each genus, a secretory parenchyma which may be vascularized and a non-secretory vascularized parenchyma. Anatomical variants observed in nectaries of different species are not consistent with the floral pollination syndromes neither with groups of pollinators. The basic structure of the nectar chamber is relatively conserved, a fact that may be explained by phylogenetic conservatism among the genera investigated. Our results revalue the role of anatomical traits for the systematics of Cactaceae.

Abstract To study the ontogeny of the extrafloral nectaries present in the inflorescences of Vigna luteola (Jacq.) Benth (Leguminosae, Phaseolinae), the location, morphology, anatomy of the earliest stages, histology of the definitive structures and ultrastructure of the secretory stage were analyzed. The extrafloral nectaries at different developmental stages were examined with light microscopy and scanning electron microscopy. The secretory stage was also examined with transmission electron microscopy. The racemose inflorescence of V. luteola has six nodes. At each node, a short globose secondary axis bears two flowers and one to three extrafloral nectaries. Each extrafloral nectary originates from the abscission of a flower bud and is formed by two differentiated zones: a ring of epidermal cells surrounding a group of longitudinally enlarged papillose central cells, both with underlying secretory parenchyma. The primary secretory tissue consists of the central cells, while the ring contributes to secretion to a lesser degree. Secretion is granulocrine, by means of exocytotic vesicles and plasmalemma invaginations. Four developmental stages succeed; the third one being the secretory. The extrafloral nectaries activity period starts when the flowers of the same secondary axis open and ceases before fruit development.

Abstract The aim of this paper is to investigate the ultrastructural events that occur during pollen grains development, with emphasis in pollen grain wall and tapetum ontogeny in Ziziphus jujuba, Z. mucronata, Paliurus spina-christi (Paliureae) and Gouania ulmifolia (Gouanieae). Anthers at different developmental stages were processed according to classic techniques for transmission electron microscopy. Differences in the number of endothecium layers and in the number of tapetal cell nuclei were found. Tapetal cells present an anastomosing tubular network and large vesicles with fibrillar content in the cytoplasm. Pollen grain development and ontogeny of pollen grain wall are similar in the four species. The number of endothecium layers, the number of nuclei of the tapetal cells and tapetal cells ultrastructure of the four species support the phylogenetic relationships previously published for the Rhamnaceae family. Tapetal vesicles with fibrillar or polysaccharide content seem to be an exclusive characteristic of the tribes Paliureae and Gouanieae. Some ultrastructural characters of the pollen grain wall development are common to other species of Rhamnaceae, such as the primexine matrix present at the microspore mother cell stage, the aperture entirely built up during the tetrad stage, the thick and fibrillar intine, and the granular infractectum.

Orbicules diversity in Poaceae. Anthers of ten species of Poaceae from the province of Buenos Aires (Argentina) were investigated with scanning and transmission electron microscopes. The orbicules can be defined as corpuscles of variable size that show the same electron-density, reaction to the dyes, autofluorescence and resistance to acetolysis as pollen exine does. The orbicules are randomly dispersed on the inner anther locule and they are often attached to a tapetal membrane. In this study, four different types and four subtypes of orbicules were identified. We conclude that the different orbicules types described in this work are representative of the studied tribes, and we suggest that the orbicules morphology may be a useful character in systematic studies.

Anteras de diez especies de Poaceae de la Provincia de Buenos Aires (Argentina) fueron investigadas con microscopio electrónico de barrido y de transmisión. Las orbículas pueden ser definidas como corpúsculos de tamaño variable que muestran la misma electrodensidad, reacción a los colorantes, autofluorescencia y resistencia a la acetólisis que la exina del grano de polen. Las orbículas se encuentran revistiendo el interior del lóculo de la antera, a menudo adheridas a una membrana tapetal. En este estudio se identificaron cuatro tipos y cuatro subtipos diferentes de orbículas. Se concluye que los distintos tipos morfológicos de orbículas descriptos en este trabajo son representativos de cada una de las tribus estudiadas, por lo que se sugiere que la morfología de estos corpúsculos podría ser un carácter utilizado en estudios sistemáticos.

Pollen morphology and the degree of pollen variability within nine species and two varieties of Oxalis species from Buenos Aires Province (Argentina) were studied using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxalis pollen grain is generally 3-colpate and the shape is prolate spheroidal, oblate spheroidal or spheroidal. The exine is microreticulate. The brochi are circular to polygonal; brochi sizes decrease near the colpi. The colpus membrane observed in unacetolysed material, is crustate or granular. The colpus length varies within a species; the largest grains are produced in stamens with long filaments and the smallest ones in stamens with short filaments. Four pollen types are distinguished by means of LM, SEM and TEM. They are recognized mostly on the basis of their colpus membrane structure. In conclusion, the morphological similarity among Oxalis species is also reflected in their pollen morphology.

The correlation between the ontogeny of Ubisch bodies and pollen development in Oxalis articulata was studied with Transmission Electron Microscopy (TEM). The ultrastructural changes observed during the different stages of development in the tapetal cells are related to Ubisch bodies, sporopollenin and pollen-kitt formation. The pro-orbicules have the appearance of lipid globuli and their formation is related to the endoplasmic reticulum of rough type (ERr). The lipid globules or pro-orbicules disappear in the mature Ubisch bodies, and the places that they occupied remain free of contents or with pollen-kitt.