Cold hardy Japanese bunching onion (Allium fistulosum L.) was used as a novel model system to examine the role of the apoplast in intracellular freezing avoidance. Since intracellular freezing avoidance is critical to both sensitive and resistant plants, non-acclimated and cold acclimated onion tissue was compared. The large 250 (length) x 50 (width) x 90 µm (thickness) intact single cell epidermal layer system allowed direct observation of the freezing process during freezing and thawing on a single cell basis in live intact tissues in non-acclimated (23/18°C) and acclimated (2 weeks at 12/4°C) plants. Under acclimation treatment, freezing resistance increased from an LT50 of -12°C at zero time to -27°C after two weeks exposure. Ice nucleation was always initiated in the apoplastic space in both non-acclimated and acclimated cells and then penetrated into the intracellular space. We provide direct evidence that lethal intracellular freezing damage was avoided in cold acclimated and CaCl2 treated cells through visible blockage of ice propagation from the apoplastic space to the intracellular region. Subsequent investigation of the apoplastic space revealed cold acclimation increased: a) the insoluble crude cell wall and pectin (galacturonic acid) content, b) total cell wall protein quantity, c) pectin methylesterase activity in the apoplastic space particularly in epidermal cells compared to non-epidermal cells, and d) the levels of un-methylated pectin. The increasing freezing resistance of Japanese bunching onion more depends on the efficiency of PME not only the increase in the amount of apoplast compositions. Collectively, these changes likely led to the observed significant reduction in cell wall permeability. In this way, freezing stress resistance may potentially be increased through avoidance of intracellular freezing by altering key factors related to apoplast permeability and blocking ice propagation across the cell wall.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The aim of this work was to determine criteria for management of nutrient solution in the production of runner tips for producing strawberry plug plants and parsley and chives for commercial mixed bunches. Two experiments were carried out at Departamento de Fitotecnia-UFSM using 2.5 dm3 polypropylene pots filled with sand, placed over 0.8m heigh benches and fertigated by drippers. The first experiment was conducted from 13 October 2011 to 10 April 2012, using strawberry mother plants cv. Camino Real and Oso Grande. Plants were fertigated by five electrical conductivities, 0.4, 0.8, 1.2, 1.6 and 2.0 dS m-1, respectively, in a (5 x 2) completely randomized factorial experimental design. Runner tips emitted by mother plants were collected weekly and counted, being discarded those necrotic. It was determined the number of leaves, crown diameter and dry mass. Runner tips from mother plants of each treatment were rooted in polystyrene trays for plug plants production. Forty five days later, crown diameter, number of expanded leaves and shoot and root dry weight of plug plants were determined. At the end of the experiment, mother plants of each treatment were also collected for dry mass determination of plant organs. The second experiment was conducted from September 12 to October 22, 2012, comparing five electrical conductivities of the nutrient solution, 0.5; 1.5; 2.0; 2.5 and 3.0 dS m-1, respectively, and eight cropping arrays. The arrays were formed by planting side by side in each pot transplants of parsley and chives from one cell of the commercial tray (1S+1C), from two cells of parsley and one of chives (2S+1C), one of parsley and two of chives (1S+2C), two of parsley and two of chives (2S+2C) and four monocropping arrays as controls: seedlings from one cell tray of parsley (1S) and one of chives (1C) and two of parsley (2S) and two of chives (2C) per pot. It was used a (5 x 8) completely randomized factorial experimental design. At the end of the experiment, plants of both species were harvested, separated and fresh (MVPA) and dry mass (MSPA) of shoot were determined. It was concluded that electrical conductivities of the nutritive solution in the range between 0.8 and 1.1 dS m-1 for growing strawberry mother plants lead to higher runner tips and plug plants production. Intercropped parsley and chives can be grown using the same nutrient solution at 2.0 dS m-1 for the commercial production of mixed bunches, while an electrical conductivity of 1.6 dS m-1 can be used for monocropped chives production. / O objetivo deste trabalho foi determinar critérios de manejo da solução nutritiva na produção de pontas de estolões para a produção de mudas de morangueiro e de salsa e cebolinha para produção de maços comerciais mistos. Dois experimentos foram realizados no Departamento de Fitotecnia da UFSM em dispositivos formados por bancadas de 0,8 m de altura com vasos de polipropileno de 2,5 dm3 preenchidos com areia e fertirrigados por fitas gotejadoras. O primeiro experimento foi realizado no período de 13 de outubro de 2011 a 10 de abril de 2012, com plantas matrizes de morangueiro das cultivares Camino Real e Oso Grande. As plantas foram fertirrigadas com cinco condutividades elétricas, 0,4; 0,8; 1,2; 1,6 e 2,0 dS m-1, respectivamente, em esquema fatorial (5 x 2) e delineamento inteiramente casualisado. As pontas de estolões emitidas pelas plantas matrizes foram coletadas semanalmente e contadas, sendo descartadas aquelas necrosadas. Foram determinados o número de folhas, o diâmetro de coroa e a massa seca. Pontas de estolões oriundas das plantas matrizes de cada tratamento foram enraizadas em bandejas de poliestireno para produção de mudas com torrão. Aos 40 dias após o enraizamento, foi determinada a taxa de formação de mudas e o diâmetro de coroa, número de folhas expandidas e massa seca da parte aérea e raízes dessas mudas. Ao final do experimento, foram coletadas também plantas matrizes de cada tratamento para determinação da massa seca dos diferentes órgãos. O segundo experimento foi realizado de 12 de setembro a 22 de outubro de 2012, no qual foram comparadas cinco condutividades elétricas, 0,5; 1,5; 2,0; 2,5 e 3,0 dS m-1, respectivamente, e oito arranjos de cultivo. Os arranjos foram formados pelo plantio lado a lado em cada vaso de mudas de salsa e de cebolinha provenientes de um alvéolo das bandejas comerciais (1S+1C); de dois alvéolos de salsa e um alvéolo de cebolinha (2S+1C); de um de salsa e dois de cebolinha (1S+2C); de dois de salsa e dois de cebolinha (2S+2C) e quatro sistemas de cultivos solteiros considerados testemunhas: mudas de um alvéolo de salsa (1S) e um de cebolinha (1C) e dois de salsa (2S) e dois de cebolinha (2C) por vaso. Foi empregado um esquema fatorial (5 x 8) em delineamento DIC. No final do experimento, as plantas de cada uma das duas espécies foram separadas e foi determinada a massa verde (MVPA) e seca (MSPA) da parte aérea. Concluiu-se que condutividades elétricas da solução nutritiva entre 0,8 e 1,1 dS m-1 possibilitam maior produção de pontas de estolões de morangueiro e formação de mudas com torrão. No cultivo consorciado de salsa e cebolinha, é possível o uso de uma mesma solução nutritiva com 2,0 dS m-1 para a formação de maços mistos, podendo a mesma solução ser empregada também no cultivo da salsa solteira. No cultivo solteiro de cebolinha, a C.E de 1,6 dS m-1 deve ser empregada.