Nectary structure is not related to pollination system in Trichocereeae cactus from Northwest Argentina.

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.

Leaf structure and ultrastructure changes induced by heat stress and drought during seed filling in field-grown soybean and their relationship with grain yield.

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.

Morphological differentiation across the invasive range in Senecio madagascariensis populations.

Invasive species are characterized by their ability to colonize new habitats and establish populations away from their native range. In this sense, these plants are expected to have plastic responses to adapt to the environmental pressures during the invasion process. Hence, the role of natural selection is essential because it might favor the occurrence of advantageous traits. However, gene flow can counteract natural selection because immigrants introduce genes adapted to different conditions, with these introductions tending to homogenize allelic frequencies. In this work, we explore the effect of natural selection in invasive populations of S. madagascariensis in Argentina. We quantified leaf area, head number, and length of internodes and inflorescence from material spanning 54 years (1962-2016) and then compared between the edge versus established ranges. Our results show differences in all the measured plant traits among the sampled areas. However, only leaf area was statistically significant, which evidences different responses under the same environmental pressures in the areas located in the edge and established ranges. On the other hand, unlike homogeneous areas, the areas characterized by phenotypically diverse individuals were related to higher dispersal ability. In this sense, long-distance dispersal between neighboring areas may have had an important role in the recorded values. Furthermore, the implications of natural selection and founder effect in the invasion of S. madagascariensis are discussed.

Floral nectaries in Sapindaceae s.s.: morphological and structural diversity, and their systematic implications.

We investigated the morphology and structure of the floral nectary in 11 Neotropical genera belonging to the subfamilies Dodonaeoideae and Paullinioideae (Sapindaceae) from southern South America representing three tribes (Dodonaeaeae, Paullinieae, and Melicocceae), in relation to other floral traits in species with contrasting morphological flower characteristics. Nectary organization was analyzed under light, stereoscopic, and scanning electron microscopes; Diplokeleba floribunda N.E. Br. was also observed using transmission electron microscopy. Our comparative data may contribute to the understanding of floral nectary evolution and systematic value in this family. The nectaries were studied in both staminate and pistillate flowers. All the floral nectaries are typical of Sapindaceae: extrastaminal, receptacular, structured, and persistent. The anatomical analysis revealed a differentiated secretory parenchyma and an inner non-secretory parenchyma; the nectary is supplied by phloem traces and, less frequently, by phloem and xylem traces. Nectar is secreted through nectarostomata of anomocytic type. The anatomical analysis showed the absence of nectary in the three morphs of Dodonaea viscosa flowers. Nectary ultrastructure is described in D. floribunda. In this species, the change in nectary color is related to progressive accumulation of anthocyanins during the functional phase. We found relatively small variation in the nectary structural characteristics compared with large variation in nectary morphology. The latter aspect agreed with the main infrafamilial groupings revealed by recent phylogenetic studies, so it is of current valuable systematic importance for Sapindaceae. In representatives of Paullinieae, the reduction of the floral nectary to 4-2 posterior lobes should be interpreted as a derived character state.

Molecular and cytogenetic characterization of an AT-rich satellite DNA family in Urvillea chacoensis Hunz. (Paullinieae, Sapindaceae).

Urvillea chacoensis is a climber with 2n = 22 and some terminal AT-rich heterochromatin blocks that differentiate it from other species of the genus. The AT-rich highly repeated satellite DNA was isolated from U. chacoensis by the digestion of total nuclear DNA with HindIII and XbaI and cloned in Escherichia coli. Satellite DNA structure and chromosomal distribution were investigated. DNA sequencing revealed that the repeat length of satDNA ranges between 721 and 728 bp, the percentage of AT-base pairs was about 72-73% and the studied clones showed an identity of 92.5-95.9%. Although this monomer has a tetranucleosomal size, direct imperfect repetitions of ~180 bp subdividing it in four nucleosomal subregions were observed. The results obtained with FISH indicate that this monomer usually appears distributed in the terminal regions of most chromosomes and is associated to heterochromatin blocks observed after DAPI staining. These observations are discussed in relation to the satellite DNA evolution and compared with other features observed in several plant groups.