HighlightArabis alpina stems have a perennial zone with secondary growth, where cambium and derivatives store high-molecular weight compounds independent of vernalization. Cytokinins are signals for the perennial secondary growth zone. 2 AbstractPerennial plants maintain their life span through several growth seasons. Arabis alpina serves as model Brassicaceae species to study perennial traits. A. alpina lateral stems have a proximal vegetative zone with a dormant bud zone, and a distal senescing seed-producing inflorescence zone.We addressed the questions of how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage, and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and sequestration of storage compounds. The inflorescence zone with only primary growth, termed annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application, cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis cytokinin-related genes represented enriched gene ontology terms and were expressed at higher level in PZ than AZ. Thus, A. alpina uses primarily the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth. ReferencesAgusti J, Lichtenberger R, Schwarz M, Nehlin L, Greb T (2011) Characterization of transcriptome remodeling during cambium formation identifies MOL1 and RUL1 as opposing regulators of secondary growth. PLoS Genet 7: e1001312 Alexa A, Rahnenfuhrer J (2010) topGO: enrichment analysis for gene ontology. R package version 2 Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ (1990) Basic local alignment search tool. J Mol Biol 215: 403-410 Anders S, Pyl PT, Huber W (2015) HTSeq-a Python framework to work with high-throughput sequencing data. Bioinformatics 31: 166-169 Andrews S (2010) FastQC: a quality control tool for high throughput sequence data (https://www.bioinformatics.babraham.ac.uk/projects/fastqc/) Ben Abdallah H, Bauer P (2016) Quantitative Reverse Transcription-qPCR-based gene expression analysis in plants.

The content of 14 C in the products of photosynthesis of the source leaf and xylem sap was investigated in kidney bean ( Phaseolus vulgaris L.) plants during the stage of mass tillering. 14 C partition was measured a day after two-minute photoassimilation of 14 ëé 2 by an individual mature leaf located in the middle part of the shoot. The source-sink relations were disturbed by the excision of all mature leaves (except the source leaf) or all growing axillary shoots. The leaves or growing axillary shoots were excised 15 min after leaf feeding with 14 ëé 2 . A day later, in plants with excised growing axillary shoots, the content of 14 C in the source leaf was by 18% higher and in those with removed leaves by 15% lower than in control plants. The next day after the excision of growing axillary shoots, radioactivity of the xylem sap increased; after defoliation, both the volume of the xylem sap and its specific radioactivity decreased. In the xylem sap of defoliated plants, the proportion of 14 C in malate decreased more than six times, whereas the proportion of 14 C in amino acids somewhat increased (1.5 times). In two days, the volume of the xylem sap exuded by treated plants became the same as in control plants and its radioactivity decreased almost by an order of magnitude but essentially did not differ in the both types of treatment. It is concluded that the processes occurring in the roots are governed by photosynthesis but its regulatory effect is limited by a photoperiod and largely depends on changes in the ratio between biosynthesis of amino acids in the roots and leaves.

A 1 μM solution of ammoniates [ZnCu(NH 3 ) n ] 2+ (CO 3 ) 2-was inserted into a cut shoot of flax with the transpiration stream of water. Analysis of the 14 C content after 14 CO 2 assimilation by the shoot showed that ammoniates increased radioactive label contents in the tissues (especially in the young leaves and stem). In the leaves the higher sucrose to hexoses ratio, an increased radioactivity of glycerate and malate and decreased incorporation of 14 C into oligosaccharides and pigments were observed. These effects were more pronounced in the young leaves. Spraying of plants with 20 mM solution resulted in an increase of plant height and leaf number.Additional key words: apoplast, assimilate transport, Linum usitatissimum, photosynthesis, physiologically active substances, plant productivity. ⎯⎯⎯⎯It is often found that high nitrogen nutrition leads to increased shoot to root mass ratio, which can be negative in the case of root crops such as cassava (Cruz et al. 2004). In the previous investigations it was shown that the reason of a relative decrease of assimilate export from leaves in plants fertilized with nitrogen was not a decrease of sucrose synthesis as a result of diverting photosynthesis primary products to the formation of nitrogen-containing compounds in the leaf, but sucrose hydrolysis in the apoplast (Chikov et al. 2001). Since in the apoplast sucrose hydrolysis occurs mainly by acid invertase it should be expected that apoplastic fluid acidity must influence this process. The validity of this conclusion was proved in the experiments with artificial changing the extracellular space acidity. Measurements of 14 CO 2 fixation rates and 14 C content in the apoplast in plants transiently placed under a bell-jar with the atmosphere containing either HCl vapour or NH 3 vapour showed (Chikov 1987) the opposite actions of the investigated factors on photosynthetic rate and the 14 C content in the leaf apoplast. The acidification suppressed 14 CO 2 fixation by the leaf, with the labelled assimilates being accumulated in the apoplast. Conversely, the ammonia vapours had some stimulating effect on photosynthesis and decreased the 14 C-labelled substances content in the apoplast. Thus, to weaken sucrose hydrolysis in the apoplast it is necessary to decrease the extracellular aqueous medium acidity. To make such a situation in the apoplast we decided to use complex compounds with the general formula of [M (NH 3 )n] +m A -m ]. It was supposed that the metal of the complex in the form of a cation surrounded with ammonia would be adsorbed on the cell walls in the apoplast (Blinda et al. 1997) and thereby would extrude H + out of the aqueous medium increasing the pH value.Furthermore, the alkalization of the apoplastic fluid may also occur when a part of NH 3 molecules goes out of the complex compounds to their environment, because the complex persists even if a part of NH 3 molecules has released. An increase in apoplastic pH after fumigation of a leaf with NH 3 was observed by Felle and Hanstein (2002). Althoug...

Perennial plants maintain their lifespan through several growth seasons. Arabis alpina serves as a model Brassicaceae species to study perennial traits. Lateral stems of A. alpina have a proximal vegetative zone with a dormant bud zone and a distal senescing seed-producing inflorescence zone. We addressed how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular-weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and the sequestration of storage compounds. The inflorescence zone with only primary growth, termed the annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis, cytokinin-related genes represented enriched gene ontology terms and were expressed at a higher level in the PZ than in the AZ. Thus, A. alpina primarily uses the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth.