Microtubule organization changes severely after mannitol and n-butanol treatments inducing microspore embryogenesis in bread wheat.

BACKGROUND: A mannitol stress treatment and a subsequent application of n-butanol, known as a microtubule-disrupting agent, enhance microspore embryogenesis (ME) induction and plant regeneration in bread wheat. To characterize changes in cortical (CMT) and endoplasmic (EMT) microtubules organization and dynamics, associated with ME induction treatments, immunocytochemistry studies complemented by confocal laser scanning microscopy (CLSM) were accomplished. This technique has allowed us to perform advanced 3- and 4D studies of MT architecture. The degree of MT fragmentation was examined by the relative fluorescence intensity quantification. RESULTS: In uni-nucleated mannitol-treated microspores, severe CMT and EMT fragmentation occurs, although a complex network of short EMT bundles protected the nucleus. Additional treatment with n-butanol resulted in further depolymerization of both CMT and EMT, simultaneously with the formation of MT aggregates in the perinuclear region. Some aggregates resembled a preprophase band. In addition, a portion of the microspores progressed to the first mitotic division during the treatments. Bi-nucleate pollen-like structures showed a high MT depolymerization after mannitol treatment and numerous EMT bundles around the vegetative and generative nuclei after n-butanol. Interestingly, bi-nucleate symmetric structures showed prominent stabilization of EMT. CONCLUSIONS: Fragmentation and stabilization of microtubules induced by mannitol- and n-butanol lead to new configurations essential for the induction of microspore embryogenesis in bread wheat. These results provide robust insight into MT dynamics during EM induction and open avenues to address newly targeted treatments to induce ME in recalcitrant species.

Progress of snow mould infection in crowns of winter rye (Secale cereale L.) is related to photosynthetic activity during cold acclimation.

Resistance to snow mould is a feature determined by multiple genes. Therefore, determining the phenotype of resistant plants is difficult as it requires an investigation over a long period of time from cold acclimation through pathogenesis. The aim of the present study was (i) to determine the characteristics of the resistant genotype and (ii) to clarify the connections between photosynthesis during cold acclimation and then pathogenesis caused by Microdochium nivale. Two inbred lines of winter rye (Secale cereale L.) differing in their susceptibility to snow mould were used in the study. After cold acclimation snow mould resistant (SMR) line was characterised by higher values of CO2 assimilation and electron transport efficiency but did not differ from snow mould susceptible (SMS) line in carboxylation rate of RuBisCO (Vcmax). Higher soluble carbohydrate accumulation, due to higher photosynthesis intensity, as well as an ABA increase at 5 days post infection (DPI) in leaves and crowns were found in SMR line during the pathogenesis period. Callose deposition was found around non-infected bundle sheets and in cortex cells at 5 DPI (at the same time point as ABA peak) only in SMR line, which probably prevented the infection of leaf initials. Early leaf initials infection in SMS line may be responsible for inhibiting leaf growth and plant regeneration after stress cessation. The results show different physiological and biochemical characteristics of the investigated lines, which can be applied in the selection of resistant genotypes and identifying genomic regions responsible for metabolic pathways increasing pathogen resistance.

Quantitative trait loci associated with androgenic responsiveness in triticale (×Triticosecale Wittm.) anther culture.

Quantitative trait loci (QTLs) associated with androgenic responsiveness in triticale were analyzed using a population of 90 DH lines derived from the F1 cross between inbred line 'Saka 3006' and cv. 'Modus', which was used in a number of earlier studies on molecular mapping in this crop. Using Windows QTL Cartographer and MapQTL 5.0, composite interval mapping (CIM) and association studies (Kruskal-Wallis test; K-W) for five androgenesis parameters (androgenic embryo induction, total regeneration and green plant regeneration ability, and two characteristics describing final androgenesis efficiency) were conducted. For the studied components of androgenic response, CIM detected in total 28 QTLs which were localized on 5 chromosomes from A and R genomes. Effects of all QTLs that were identified at 2.0 or above of the LOD score explained 5.1-21.7 % of the phenotypic variation. Androgenesis induction was associated with seven QTLs (LOD between 2.0 and 5.8) detected on chromosomes 5A, 4R, 5R and 7R, all of them confirmed by K-W test as regions containing the markers significantly linked to the studied trait. What is more, K-W test revealed additional markers on chromosomes: 5A, 2BL, 7B and 5R. Both total and green regeneration ability were controlled by genes localized on chromosome 4A. Some of the QTLs that affected final androgenesis efficiency were identical with those associated with androgenic embryo induction efficiency, suggesting that the observed correlation may be either due to tight linkage or to pleiotropy. Key message Five regions of the triticale genome were indicated as revealing significant marker/trait association. Markers located in these regions are potentially useful for triticale breeding through marker-assisted selection.