Mango is a commercial fruit crop in different parts of the tropical and subtropical world. Commercially important monoembryonic varieties are propagated through grafting onto rootstock seedlings of polyembryonic genotypes that plays an important role in sustained growth and production. Use of salt tolerant genotypes as rootstock to combat the adverse effect of salinity could be helpful for commercial mango production in salt affected areas. Current study was carried out to elucidate the effect of salinity stress induced by NaCl + CaCl2 (1:1 w/w) at 0, 25, 50 and 100 mM concentrations in irrigation water on candidate polyembryonic mango genotypes namely EC-95862, Bappakkai, Vellaikolamban, Nekkare, Turpentine, Muvandan, Kurukkan, Kensington, Olour, Manipur, Deorakhio, Vattam, Mylepelian, Sabre and Kitchener. We studied the morpho-physiological changes of these seedlings under salinity induced stress for determining their relative tolerance by assessing growth parameters such as plant height, number of leaves, leaf area, inter-nodal length, fresh weight of shoot, fresh weight of root, dry weight of shoot, dry weight of root, stem diameter and physiological parameters like photosynthetic rate, transpiration rate, stomatal conductance, number of stomata and stomata length and width, in addition to ABA content in leaves. Our results clarifies that the polyembryonic genotypes Turpentine, Deorakhio Olour and Bappakkai showed less reduction in terms of growth and better maintenance of gas exchange status under higher level of salinity.
Anti-oxidative system in plants comprising of enzymatic and non-enzymatic antioxidants imparts stress tolerance by scavenging/detoxification of excess reactive oxygen species (ROS) produced under high temperature stress. Present investigation deals with the estimation of metabolites and anti-oxidative enzyme activities in four inbred maize lines; NSJ221, NSJ189, PSRJ13099 and RJR270 in response to high temperature stress imposed at reproductive stage by staggered sowing. An increase in H2O2 and malondialdehyde (MDA) was observed in all the genotypes, however the increase was higher in PSRJ13099 and RJR270. The activities of studied enzymes increased in NSJ189 and NSJ221 while a decrease was observed in PSRJ13099 and RJR270. Under heat stress isoforms of SOD increased in NSJ189 and NSJ221 while a concomitant decrease was observed in PSRJ13099 and RJR270. Two new SOD-isoforms were also observed in NSJ221. GPX showed more number of high mobility isoforms with low activity in NSJ221 and less mobile isoforms with higher activity in both NSJ189 and NSJ221. Whereas, PSRJ13099 and RJR270 showed decrease band intensity of less mobile GPX-isoforms under heat stress. Activity of CAT-isoforms increased to a similar extent across the genotypes under heat stress. In case of non-enzymatic antioxidants, non-protein thiols increased in all the genotypes while the level of carotenoids depleted in all the genotypes except NSJ221. Ascorbate (AsA) levels depleted in PSRJ13099 and RJR270 and increased in NSJ189 and NSJ221 under heat stress. Understanding the intricate regulatory pathways in crop plants under heat stress will help in developing genotypes with enhanced stress tolerance.
Over 80 samples of fossil woods were collected from numerous outcrops of the Río Turbio Formation, southwestern Patagonia. Preservation of the woods is variable and only about half of these samples could be identified to genus level. The assemblage consists of six types of conifers and four types of dicotyledons, one of them a new species of Caldcluvioxylon (Cunoniaceae). We provide an emended diagnosis of Caldcluvioxylon. A previously described fossil wood from this stratigraphic unit, thought to have affinity with Proteaceae, was re-examined and is described herein as Scalarixylon romeroi sp.nov. Other families recognized in the Río Turbio Formation wood assemblage are Araucariaceae, Podocarpaceae, and Nothofagaceae. Differences in the taxonomic composition of the upper and lower members of the Río Turbio Formation are consistent with the age difference between them according to recent isotopic dating. The diversity of fossil wood is also consistent with the fossil leaves and pollen from each stratigraphic level and most of the taxa are shared with coeval Antarctic fossil wood floras.
Studies of anatomically preserved fossils provide a wealth of information on the evolution of plant vascular systems through time, from the oldest evidence of vascular plants more than 400 million years ago to the rise of the modern angiosperm-dominated flora. In reviewing the key contributions of the fossil record, we discuss knowledge gaps and major outstanding questions about the processes attending the evolution of vascular systems. The appearance and diversification of early vascular plants in the late Silurian-Devonian was accompanied by the evolution of different types of tracheids, which initially improved the hydraulics of conduction but had less of an effect on mechanical support. This was followed in the Devonian and Carboniferous by an increase in complexity of the organization of primary vascular tissues, with different types of steles evolving in response to mechanical, hydraulic, and developmental regulatory constraints. Concurrently, secondary vascular tissues, such as wood, produced by unifacial or bifacial cambia are documented in a wide array of plant groups, including some that do not undergo secondary growth today. While wood production has traditionally been thought to have evolved independently in different lineages, accumulating evidence suggests that this taxonomic breadth reflects mosaic deployment of basic developmental mechanisms, some of which are derived by common ancestry. For most of vascular plant history, wood contained a single type of conducting element: tracheids (homoxyly). However, quantitative (e.g. diameter and length) and qualitative (e.g. pitting type) diversity of these tracheids allowed various taxa to cover a broad range of hydraulic properties. A second type of conducting elements, vessels, is first documented in an extinct late Permian (c. 260 Ma) group. While the putative hydraulic advantages of vessels are still debated, wood characterized by presence of vessels (heteroxyly) would become the dominant type, following the diversification of angiosperms during the Cretaceous.
Angiosperm wood from the Miocene Landslip Hill silcrete, Southland, New Zealand is described. It is characterised by solitary vessels of two distinct size classes; rays of two size classes alongside aggregate rays; simple perforation plates; and axial parenchyma in tangential bands up to three cells wide. The wood has features similar to Casuarinaceae and is described here as a new species, Casuarinoxylon ildephonsi. The fossils were collected as isolated fragments of wood; there is no directly associated cladode or cone material although isolated fragments of these are common elsewhere in the Landslip Hill silcrete. This is the second record of fossil Casuarinaceae wood from New Zealand and the first sample to be anatomically described. Currently, Casuarinaceae does not occur in New Zealand. Casuarinoxylon ildephonsi would have grown in a warm temperate to subtropical climate on an open deltaic floodplain.
The origin of xylem in the Silurian was a major step in plant evolution, leading to diverse growth forms with various mechanical and hydraulic properties. In the fossil record, these properties can only be investigated using models based on extant plant physiology. Regarding hydraulics, previous studies have considered either the properties of a single tracheid or of a set of independent tubes. Here, we use the analogy between the flow of water under tension in a plant and an electrical circuit to develop an extension of Wilson’s single tracheid model to the tissue scale. Upscaling to the tissue-level allows considering wood as a heterogeneous tissue by taking into account differences in tracheid density and the presence of rays. The new model provides a more biologically accurate representation of fossil wood hydraulic properties. The single tracheid and new tissue models are applied to two conspecific specimens of Callixylon (Progymnospermopsida, Archeopteridales) from the Late Devonian of Morocco. Differences are shown at the tissue level that cannot be suspected at the single tracheid level. Callixylon represents the first trees with a conifer-like wood and is a major component of Late Devonian floras world-wide. Our results show that the anatomical disparity of its wood might have led to hydraulic plasticity, allowing growth in various environmental conditions. More generally, the new tissue-model suggests that the various combinations of tracheid and ray sizes present in Palaeozoic plants might have led to a higher variety of ecophysiologies than suspected based solely on the properties of individual tracheids.
Thousands of silicified wood fragments were recently collected from the middle Cenomanian of Vienne in western France at less than 10 km away from a historical locality where in 1870 the French geologist Alphonse Le Touzé de Longuemar reported silicified wood. The plant assemblage is very diverse, and includes several species of ferns, conifers, and angiosperms. We describe and discuss the systematic affinities of a new vesselless angiosperm. Many of its characters are shared by extant and fossil Winteraceae. Nevertheless, the absence of uniseriate rays makes the anatomy of these specimens unique. Its combination of characters justifies the establishment of a new genus of vesselless fossil angiosperm wood of uncertain affinity, Sherwinoxylon gen. nov.
Adaptive variation of plant species is best evaluated under environmental gradients. Silybum marianum is a native to the Mediterranean basin, distributed continuously along an aridity gradient from northern Israel to the edge of the Negev desert. To elucidate the adaptive significance of traits associated with proximity to the desert and with increasing levels of aridity, we compared northern populations from the mesic Mediterranean end of the aridity gradient with southern, adjacent to the Negev desert populations, from the arid end. The F1 self-progeny of all populations were evaluated under open field conditions. Plants originated from southern populations grew taller and narrower, completed their life cycle earlier, and produced more abundant, smaller achenes, with a higher content of polyphenols, which grew into smaller seedlings. Correlative analysis revealed a latitudinal cline towards the desert, of a longer life cycle, and fewer, heavier, better germinating achenes, which grew into larger seedlings. We concluded that the proximity to the desert was reflected in the appearance of genotypes with improved chances of survival under arid conditions and with higher contents of polyphenols.