Light-induced STOMAGEN-mediated stomatal development in Arabidopsis leaves.

The initiation of stomata, microscopic valves in the epidermis of higher plants that control of gas exchange, requires a co-ordinated sequence of asymmetric and symmetric divisions, which is under tight environmental and developmental control. Arabidopsis leaves grown under elevated photosynthetic photon flux density have a higher density of stomata. STOMAGEN encodes an epidermal patterning factor produced in the mesophyll, and our observations indicated that elevated photosynthetic irradiation stimulates STOMAGEN expression. Our analysis of gain and loss of function of STOMAGEN further detailed its function as a positive regulator of stomatal formation on both sides of the leaf, not only in terms of stomatal density across the leaf surface but also in terms of their stomatal index. STOMAGEN function was rate limiting for the light response of the stomatal lineage in the adaxial epidermis. Mutants in pathways that regulate stomatal spacing in the epidermis and have elevated stomatal density, such as stomatal density and distribution (sdd1) and too many mouth alleles, displayed elevated STOMAGEN expression, suggesting that STOMAGEN is either under the direct control of these pathways or is indirectly affected by stomatal patterning, suggestive of a feedback mechanism. These observations support a model in which changes in levels of light irradiation are perceived in the mesophyll and control the production of stomata in the epidermis by mesophyll-produced STOMAGEN, and whereby, conversely, stomatal patterning, either directly or indirectly, influences STOMAGEN levels.

Stomatal and pavement cell density linked to leaf internal CO2 concentration.

BACKGROUND AND AIMS: Stomatal density (SD) generally decreases with rising atmospheric CO2 concentration, Ca. However, SD is also affected by light, air humidity and drought, all under systemic signalling from older leaves. This makes our understanding of how Ca controls SD incomplete. This study tested the hypotheses that SD is affected by the internal CO2 concentration of the leaf, Ci, rather than Ca, and that cotyledons, as the first plant assimilation organs, lack the systemic signal. METHODS: Sunflower (Helianthus annuus), beech (Fagus sylvatica), arabidopsis (Arabidopsis thaliana) and garden cress (Lepidium sativum) were grown under contrasting environmental conditions that affected Ci while Ca was kept constant. The SD, pavement cell density (PCD) and stomatal index (SI) responses to Ci in cotyledons and the first leaves of garden cress were compared. (13)C abundance (δ(13)C) in leaf dry matter was used to estimate the effective Ci during leaf development. The SD was estimated from leaf imprints. KEY RESULTS: SD correlated negatively with Ci in leaves of all four species and under three different treatments (irradiance, abscisic acid and osmotic stress). PCD in arabidopsis and garden cress responded similarly, so that SI was largely unaffected. However, SD and PCD of cotyledons were insensitive to Ci, indicating an essential role for systemic signalling. CONCLUSIONS: It is proposed that Ci or a Ci-linked factor plays an important role in modulating SD and PCD during epidermis development and leaf expansion. The absence of a Ci-SD relationship in the cotyledons of garden cress indicates the key role of lower-insertion CO2 assimilation organs in signal perception and its long-distance transport.

Statistical correlations of primer thermodynamic stability DeltaG degrees for enhanced flax ISSR-PCR cultivar authentication.

We revealed four statistically significant correlations related to inter-simple-sequence repeat (ISSR) patterns: (1) between thermodynamic free energy DeltaG degrees of ISSR primer sequence and PCR reamplification intensity (dA(i)), (2) between free energy DeltaG degrees of ISSR primer sequence and PIC coefficient quantifying the polymorphism of ISSR patterns, (3) and (4) between free energy DeltaG degrees of anchor sequence of primer and the number of total, and polymorphic bands in ISSR patterns, respectively. Methodological recommendations for effective ISSR primer design were inferred based on revealed correlations. In particular, free energy of ISSR primer sequence is recommended to be DeltaG degrees > 160 kJ/mol of interaction and free energy of flanking anchor sequence in primer to be around DeltaG degrees = 28 kJ/mol of interaction to produce ISSR patterns displaying maximum polymorphism of flax germplasm.

Insertion of a reamplification round into the ISSR-PCR protocol gives new flax fingerprinting patterns.

We expanded the basic ISSR-PCR protocol by an additional PCR reamplification round in order to detect whether increased PCR productivity would give new bands in ISSR patterns. We found that the reamplification step had a prominent impact on the quality of the inter-simple-sequence repeat (ISSR) PCR patterns of flax, depending on the particular primer used for PCR amplification. We could clearly distinguish between two types of reamplification effect. Most ISSR primers (16 out of 21) gave no reamplification effect as usual, but five primers (23.8%) provided a new ISSR fingerprinting pattern after the 2nd reamplification round, leaving the previous 1st round pattern completely blank. Therefore, we recommend the expansion of a basic ISSR-PCR protocol for another reamplification round in order to mine out full the fingerprinting potential from ISSR-PCR method.