Chlorophyllide-a-Oxygenase (CAO) deficiency affects the levels of singlet oxygen and formation of plasmodesmata in leaves and shoot apical meristems of barley

Abstract

In plants, organogenesis and specification of cell layers and tissues rely on precise symplastic delivery of regulatory molecules via plasmodesmata. Accordingly, abundance and aperture of plasmodesmata at individual cell boundaries should be controlled by the plant. Recently, studies in Arabidopsis established reactive oxygen species as major regulators of plasmodesmata formation and gating. We show that in a barley mutant deficient in the synthesis of chlorophyll b, the numbers of plasmodesmata in leaves and in the shoot apical meristem are significantly higher than in the corresponding wild type, probably due to redox imbalance in the mutant. The resulting disturbance of symplasmic transport is likely to be the reason for the observed delayed floral transition in these mutants. In plants, plasmodesmata (PD) are indispensable regulators of cell-to-cell communications. 1 The function of meristems as well as the specification of cell layers and tissues during organogenesis rely on the symplasmic transport of regulatory molecules such as miRNAs, transcription factors or their transcripts.2 For instance, PD serve for cell-to-cell transport of the homeodomain-containing meristem regulators WUS and KNOX in shoot apical meristems (SAMs), and of floral homeotic MADS-box proteins in inflorescence meristems.3 Leaves are determinate organs the main function of which lies in the production and release of photosynthates to other plant organs. However, leaves are also the source of many signals which spread over the symplasmic route. For instance, Flowering locus T (FT) is synthesized in phloem companion cells in leaves and moves systemically to SAMs where it initiates floral transition upon unloading via PD. 4 Most likely, movement and activity of non-cell-autonomous transcription factors are controlled by developmental changes of the numbers and functional state of PD. 5,3 At the same time, we know relatively little not only about the fine structure of PD and mechanisms of protein translocation via PD, 6,7 but also about how plants control numbers and states of PD at individual cell boundaries. One of the factors involved in these processes could be the plant hormone cytokinine.8 Recent studies provided a major breakthrough in the elucidation of mechanisms regulating PD formation in plant cells. They revealed that the production of reactive oxygen species (ROS) by cellular organelles can differentially influence the formation of PD as well as their aperture. 9,10,11,12 Mutations in a gene encoding the plastid-localized thioredoxin m led to an increase in ROS and a decrease in PD conductivity in Arabidopsis roots; the mutation could be mimicked by application of methyl viologen.9 An opposite effect, namely an increase in PD conductivity, was observed in the ise1 mutant which carries a defect in a mitochondrial RNA helicase; plants defective for ISE1 also exhibited increased ROS production. 13The formation of secondary plasmodesmata was enhanced in the ise1 mutant and also in a mutant lacking the plastid RNA helicase...

Leaf Epidermis: The Ambiguous Symplastic Domain

“…Different letters indicate significant differences at p < 0.05 according to one-way ANOVA with post hoc Tukey's test. Data for barley are reproduced from Dmitrieva et al ( 2017 ). Micrographs show PD in one of the Solanum tuberosum apices examined.…”

Plastid translation is essential for lateral root stem-cell patterning in Arabidopsis thaliana

“…We previously showed that sucrose-sensitive developmental process of rfc3 can be traced back to primary root growth rather than to LR developmental processes ( Horiguchi et al, 2003 ). Although how plastid function ensures LR development should be investigated in a future study, it is interesting to note that plastid function (or dysfunction) influences symplasmic communication and spatial organization of the root apical meristem ( Benitez-Alfonso et al, 2009 ; Burch-Smith et al, 2011 ; Stonebloom et al, 2012 ; Dmitrieva et al, 2017 ). The intercellular movement of key transcription factors, such as SHORT ROOT (SHR) and WOX5 ( Nakajima et al, 2001 ; Pi et al, 2015 ), and symplasmic communication in the stem cell niche ( Liu et al, 2017 ), are crucial for establishing and maintaining the root apical meristem.…”

Singlet Oxygen in Plants: Generation, Detection, and Signaling Roles

“…Usually, a buffered SOSG solution with a final concentration of 5-100 µM is introduced into leaves or seedlings by means of vacuum-infiltration [94,125]. SOSG was described as not being able to penetrate cell membranes [126]; however, other authors reported that in high concentrations, SOSG can enter cells and accumulate in the nucleus [121,122].…”