Ana Vuleta

How do plants cope with oxidative stress in nature? A study on the dwarf bearded iris (Iris pumila)

Oxidative stress results from incongruity between the generation of toxic reactive oxygen species (ROS) and the availability of their scavengers—antioxidants. Although the short-term effects of this phenomenon are attracting much scientific attention, oxidative stress may influence an organism’s metabolism over the long (evolutionary) time scale as well. To disentangle the impact of strong light intensity from co-occurring abiotic stresses in creating adaptive responses in antioxidants and heat shock proteins (Hsps), an environment manipulation experiment was performed using a xerophyte clonal monocot, Iris pumila, native to semi-arid grasslands at the Deliblato Sands. This species is very tolerant to the combined effect of extreme abiotic stressors such as high light intensity, elevated soil surface temperatures, and scarcity of water, which commonly takes place in its natural habitats during the summer. By shading half of each selected clone, leaving the other half sun-exposed, we contrasted short-term effects of reduced daylight intensity with long-term effects of photo-oxidative stress. In both light treatments, the enzymatic activities of SOD and APX antioxidants were similar in magnitude, whereas those of CAT and POD significantly decreased in exposed compared to shaded leaves. Moreover, exposed leaves expressed a unique CAT isoform that differed biochemically from two CAT isoforms observed in shaded leaves. The content of non-enzymatic antioxidants, carotenoids (Car), remained constant with the reduction of light intensity, but their ratio to total chlorophylls (Chl) significantly decreased compared to that expressed in full sunlight. The abundance of Hsps was considerably greater in exposed than in shaded leaves, especially regarding the inducible isoforms, Hsp70 and Hsp90a, as were their proportions in relation to the constitutively expressed Hsp90b isoform. The presented results, thus, indicate that adaptive metabolic responses of I. pumila leaves to photo-oxidative stress entailed the high activity of two key enzymatic antioxidants, SOD and APX and the expression of a light-resistant CAT—to counteract the stress-mediated ROS accumulation, the increased Car to Chl ratio—to adjust the photosynthetic apparatus to the high light conditions, as well as the accelerated biosynthesis of heat shock proteins Hsp70 and Hsp90—to preserve the cellular proteostasis.

Belowground infections of the invasive Phytophthora plurivora pathogen enhance the suitability of red oak leaves to the generalist herbivore Lymantria dispar

1. Globally, vast areas of forest are currently threatened by Lymantria dispar L. and Phytophthora species, which cause widespread declines and cascading ecological impacts. One important aim of evolutionary and ecological studies is to understand their interactions.

Phenotypic plasticity in response to environmental heterogeneity contributes to fluctuating asymmetry in plants: first empirical evidence

Fluctuating asymmetry (FA) is widely used to quantify developmental instability (DI) in ecological and evolutionary studies. It has long been recognized that FA may not exclusively originate from DI for sessile organisms such as plants, because phenotypic plasticity in response to heterogeneities in the environment might also produce FA. This study provides the first empirical evidence for this hypothesis. We reasoned that solar irradiance, which is greater on the southern side than on the northern side of plants growing in the temperate zone of the Northern Hemisphere, would cause systematic morphological differences and asymmetry associated with the orientation of plant parts. We used geometric morphometrics to characterize the size and shape of flower parts in Iris pumila grown in a common garden. The size of floral organs was not significantly affected by orientation. Shape and particularly its asymmetric component differed significantly according to orientation for three different floral parts. Orientation accounted for 10.4% of the total shape asymmetry within flowers in the falls, for 11.4% in the standards and for 2.2% in the style branches. This indicates that phenotypic plasticity in response to a directed environmental factor, most likely solar irradiance, contributes to FA of flowers under natural conditions. That FA partly results from phenotypic plasticity and not just from DI needs to be considered by studies of FA in plants and other sessile organisms.

Geometric morphometrics of functionally distinct floral organs in Iris pumila: Analyzing patterns of symmetric and asymmetric shape variations

The Iris flower is a complex morphological structure composed of two trimerous whorls of functionally distinct petaloid organs (the falls and the standards), one whorl of the stamens and one tricarpellary gynoecium. The petal-like style arms of the carpels are banded over the basal part of the falls, forming three pollination tunnels, each of which is perceived by the Iris pollinators as a single bilaterally symmetrical flower. Apart from the stamens, all petaloid floral organs are preferentially involved in advertising rewards to potential pollinators. Here we used the methods of geometric morphometrics to explore the shape variation in falls, standards and style arms of the Iris pumila flowers and to disentangle the symmetric and the asymmetric component of the total shape variance. Our results show that symmetric variation contributes mostly to the total shape variance in each of the three floral organs. Fluctuating asymmetry (FA) was the dominant component of the asymmetric shape variation in the falls and the standards, but appeared to be marginally significant in the style arms. The values of FA indexes for the shape of falls (insects’ landing platforms) and for the shape of standards (long-distance reward signals) were found to be two orders of magnitude greater compared to that of the style arms. Directional asymmetry appeared to be very low, but highly statistically significant for all analyzed floral organs. Because floral symmetry can reliably indicate the presence of floral rewards, an almost perfect symmetry recorded for the style arm shape might be the outcome of pollinator preferences for symmetrical pollination units. https://doi.org/10.2298/abs160912086R Received: July 20, 2016; Revised: September 12, 2016; Accepted: September 21, 2016; Published online: October 5, 2016 How to cite this article: Radovic S, Urosevic A, Hocevar K, Vuleta A, Manitasevic-Jovanovic S, Tucic B. Geometric morphometrics of functionally distinct floral organs in Iris pumila : Analyzing patterns of symmetric and asymmetric shape variations. Arch Biol Sci. 2017;69(2):223-31.

Does Environmentally Contingent Variation in the Level of Molecular Chaperones Mirror a Biochemical Adaptation to Abiotic Stress

As Hochachka and Somero emphasized in their seminal book “Biochemical Adaptation: Mechanism and Process in Physiological Evolution“, the key question to be posed in the study of biochemical adaptation is: “How have living systems, which are based on a common set of biochemical structures and processes and subject to a common set of physical-chemical lows, been able to adapt to the enormously wide spectrum of environmental conditions found in the biosphere?“ (Hochachka & Somero, 2002). Given that the biosphere encompasses habitats with tremendously diverse combinations of physical, chemical, and biotic environmental factors, it seems reasonably to believe that the diversity of life forms that are observable in these habitats is the outcome of adaptations which have evolved to permit organisms the exploitation of nearly all land and water areas around the globe (Hochachka & Somero, 2002).