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.     

Cytological features of developing embryogenic callus and somatic embryos of Iris pumila L. and Iris setosa Pall

Abstract

Cytological examination during somatic embryogenesis in Iris pumila L. and Iris setosa Pall, were performed using light and electron microscopy. The first sign of the cellular differentiation in the initial embryogenic callus (EC; stage 1) of both Iris species was the formation of short and elongated cell types. After the onset of embryogenesis, short cells divided producing a mass of densely packed meristematic cells, closely connected with numerous plasmodesmata. Further differentiation into globular embryos (GE) led to a loss of plasmodesmata and cell separation. In vacuolated elongated cells, cytoplasm was located near the wall and around the nucleus. In both cell types amyloplasts and small mitochondria with poorly developed crystae were abundant.

Cell of GE (stage 2) contained an increased number of mitochondria and plastids comparing to those from stage 1, indicating further differentiation. Thylakoids and starch grains were observed within the plastids, while the number of cristae within the mitochondria was increasing.

In cells of embryos with coleoptile (ECl) (stage 3), plastids differentiated into chloroplasts with thylakoids. In all stages of cell differentiation, short and long cisternae of endoplasmic reticulum with ribosomes were seen. Activity of dictyosomes was increased in stages 1 and 2, then reduced in stage 3.

Ultrastructure of EC cells was identical to that of proembryogenic cells, i.e. of early GE. Ultrastructural appearance of GE cells was identical in both Iris species, but evident, and increasing, differences in mitochondria and plastids were observed between GE and ECl embryos.The presence of bi-, three- and eight- cell proembryos demonstrates that they originate from a single cell in both Iris species.     

国产13种鸢尾属植物的核型研究

对中国产13种鸢尾属Iris植物进行了核型研究。其中中甸鸢尾I.subdichotoma、长葶鸢尾I.delavayi、大锐果鸢尾I.cuniculiformis为中国特有。大锐果鸢尾的染色体数目及核型为首次报道,核型公式为2n=22=4m 6sm 12st(2SAT)。长管鸢尾I.dolichosiphon的核型为首次报道,核型公式为2n=22=4m 12sm 6st。中甸鸢尾的染色体数目为新报道,核型公式为2n=42=20m 22sm。矮紫苞鸢尾I.ruthenicavar.nana的染色体数目为新报道,3个居群的染色体数目均为2n=42,核型公式分别为中甸居群2n=42=30m 12sm(2SAT),丽江甘海子居群2n=42=28m 14sm(2SAT),中甸尼西居群2n=42=36m 6sm(4SAT)。结合以往的细胞学研究结果,显示尼泊尔鸢尾亚属subgen.Nepalensis是一个染色体数目变化较大的类群,其中的中甸鸢尾可能是联系野鸢尾属Pardanthopsis与尼泊尔鸢尾亚属的重要类群。已报道的紫苞鸢尾I.ruthenica染色体数目为2n=84,与我们所研究的变种矮紫苞鸢尾(2n=42)呈倍性关系,通过与相邻类群的分析比较,认为紫苞鸢尾应是由二倍体类群演化而来。还对鸢尾属内染色体数目的变化和核型进化的趋势进行了探讨。     

Dams and canyons disrupt gene flow among populations of a threatened riparian plant

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