Content uploaded by Murat Deveci
Author content
All content in this area was uploaded by Murat Deveci on Dec 13, 2015
Content may be subject to copyright.
Cold resistance of kohlrabi (Brassica oleracea var. gongylodes)
Abstract
In this study, two F1 hybrid Kohlrabi cultivars (Quickstar and Rapidstar) were tested for their cold resistance at four different plant development stages (seedling, tuber formation, tuber development and harvest stages), and at three different low temperatures (0, -5, -10 °C). By these cold temperature tests, changes in electricity conductivity and membrane permeability were examined. Trials were organised according to the randomised block design with three replications. Mean values were used in estimating vitality ratio (%). Cold tests also show that Quickstar becomes to be more sensitive after tuber development stage, but in Rapidstar, sensitivity starts by the tuber formation stage which is an earlier stage than other.
This chapter is about Brassica's seed mmorphology, maturity, quality, dormancy status.
The effect of modified atmosphere packaging (MAP) on kohlrabi (Brassica olerace L. gongulodes group)'s quality and antioxidant molecule during storage was examined to determine the optimal film package for maintaining freshness. To extend shelf life, MAP was tested using PE 50 μm and oriented polypropylene (OPP) films with oxygen transmission rate (OTR) at 3,000, 10,000, 15,000 mL/m2/day/atm. The OPP film packaging with modified oxygen transmission rate showed a delay in a weight loss and extended storage period. The package with OTR 3000 attained the desired gas composition of O2 3.2-6.7 kPa and CO2 13.1-19.8 kPa, in storage at room temperature. Kohlrabi stored in this package showed the lowest weight loss and the highest visual quality. Deterioration and off-odor were developed more rapidly in PE 50 μm towards the end of the storage at room temperature. However, there are no differences among OTR films in visual quality and off-odor until 60 days at cold storage. Vitamin C content of kohlrabi was reduced rapidly in OTR 15000 with high transmission rate and showed less loss in PE 50 μm and OTR 3000 in both room temperatures and cold storage. Results revealed that an OPP film with OTR 3000 extended the shelf life of kohlrabi in storage with maintained quality and vitamin C.
Quality of kohlrabi stems ( Brassica oleracea var. gongylodes L.) kept in cold storage
Two green kohlrabi cultivars, ‘White Delikates’ and ‘Korist’ F 1 , were kept in cold storage at a temperature of 2°C and a relative humidity of 95%. Natural mass losses were measured at monthly intervals and dry matter content, soluble sugars, L-ascorbic acid and isothiocyanates were analysed. During five months of storage, very low losses of kohlrabi mass were detected. The decrease in dry matter during that time was between 15 and 18%. After a brief increase, soluble sugar content decreased during storage, and in March, 50% of the initial sugar content was calculated for ‘Delikates’ kohlrabi flesh and 65% for ‘Korist’. L-ascorbic acid was well preserved in the kohlrabi, since 90% remained after storage was completed. The isothiocyanate content changed little and the vegetable remained a good source of these compounds throughout the storage period.
A simple reproducible procedure is described for assessing frost injury of potato foliage, involving controlled freezing of excised leaflets and measurement of leached electrolytes. Test results are shown for 5 tuber-bearing Solarium species representing a wide range of frost tolerance. The test can be used in selection and breeding for frost tolerance in potato.
Cold-hardened crowns of winter wheat (Triticum aestivum L.) and a winter rye (Secale cereale L.) readily dehardened upon exposure to warm temperatures. Crowns dehardened at a faster rate at 20 C than at 10 and 15 C. Dehardened plants were capable of rehardening in a short period of time upon exposure to cold-acclimating conditions. In all the dehardening studies, there was a high positive correlation between cold survival and water content of the crowns. Plants collected in the fall and stored at −2.5 C maintained the same level of hardiness for 17 wk.
Onion (Allium cepa L.) bulbs were subjected for 12 days to either a moderate freeze (-4 C) or a severe freeze (-11 C). They were then thawed slowly over ice. During 7 to 12 days following the thaw, the injury progressed with time in the severely frozen bulbs, but appeared completely repaired in the moderately frozen bulbs. This was shown by the following post-thawing changes.Infiltration of the intercellular spaces increased from 80 to 90% to 100% after the severe freeze, and decreased from 30 to 50% to zero after the moderate freeze. All of the cells were alive immediately after thawing whether the freeze was moderate or severe. Corresponding to the infiltration results 7 to 12 days later, many to most were dead following the severe freeze, all were alive following the moderate freeze.The conductivity of the effusate from pieces of bulb tissue increased after the severe freezing, and decreased after the moderate freezing. The concentration of K(+), total solutes, and sugars in the effusate paralleled the conductivity changes. Neither the pH of the effusate nor the permeability of the cells (as long as cells were living) to water was changed following either the severe or the moderate freezes. Some treatments of the thawed tissue following the severe freeze halted the progress of injury.The above results indicate that the semipermeable properties of the cell are uninjured but that the ion and sugar transport mechanism is damaged by freezing. Most likely the primary injury is to the active transport mechanism involved in their transport. It must be concluded that the final injury following freezing and thawing cannot be evaluated from the degree of infiltration or the conductivity of the effusate immediately after thawing, since injury may progress or recede following the thawing.
Spinach plants (Spinacia oleracea L.) were frost-hardened by cold-acclimation to 1° C or kept in an unhardy state at 20°/14° C in phytotrons. Detached leaves were exposed to temperatures below 0°C. Rates of photosynthetic CO2 uptake by the leaves, recorded after frost treatment, served as a measure of freezing injury. Thylakoid membranes were isolated from frost-injured leaves and their photosynthetic activities tested. Ice formation occurred at about-4° to-5° C, both in unhardened and cold-acclimated leaves. After thawing, unhardened leaves appeared severely damaged when they had been exposed to-5° to-8° C. Acclimated leaves were damaged by freezing at temperatures between-10° to-14° C. The pattern of freezing damage was complex and appeared to be identical in hardened and unhardened leaves: 1. Inactivation of photosynthesis and respiration of the leaves occurred almost simultaneously. 2. When the leaves were partly damaged, the rates of photosynthetic electron transport and noncyclic photophosphorylation and the extent of light-induced H(+) uptake by the isolated thylakoids were lowered at about the same degree. The dark decay of the proton gradient was, however, not stimulated, indicating that the permeability of the membrane to-ward protons and metal cations had not increased. 3. As shown by partial reactions of the electron transport system, freezing of leaves predominantly inhibited the oxygen evolution, but photosystem II and photosystem I-dependent electron transport were also impaired. 4. Damage of the chloroplast envelope was indicated by a decline in the percentage of intact chloroplasts found in preparations from injured leaves. The results are discussed in relation to earlier studies on freezing damage of thylakoid membranes occurring in vitro.
Low-temperature scanning electron microscopy was used to examine fracture faces in leaf blades taken from well-watered or drought-stressed barley (Hordeum vulgare L. cv. Mazurka) seedlings. The leaf blades were freeze-fixed while hydrated and were examined with or without gold-coating. There were 'droplets' (with a smooth surface at the resolution achieved) on the surface of cell walls in leaf blades (0.91 g(-1) water content) from well-watered seedlings grown in an environment of 67% relative humidity. These were mainly on the vascular bundle sheath, the guard and subsidiary cells, and on some mesophyll cells around the substomatal cavity and between the stoma and vascular bundle. The droplets occurred, more abundantly, in the same places in seedlings from 100% relative humidity. They occurred on a few guard cells from wilting leaf blades (0.81 g·g(-1) water content) and were absent from severely drought-stressed leaf blades (0.15 g·g(-1) water content). The droplets sublimed at the same moment as both water which was in leaf cells and water which was allowed to condense (after freeze-fixation) on the wall surface. It is suggested that the droplets are aqueous. Their possible origin and importance is discussed.
The frost hardiness of many plant species can be increased by exposing plants to low, non-freezing temperatures. It has been shown that at least in some herbaceous mono- and dicotyledonous species, hardening can also be induced by treating plants with NaCl at otherwise non-hardening temperatures. In the present investigation, the roots of approximately six-week-old spinach (Spinacia oleracea L.) seedlings were exposed to a 300 mM NaCl solution. Frost hardiness of the leaves, measured by the electrolyte-leakage method, increased by 2.3C over a 24-h salt-stress period. Salt uptake, as measured with a chloride-sensitive electrode in leaf homogenates, was rapid over the first 7 h of salt exposure and then slowed down. There was no correlation between the chloride content of the leaves and their frost hardiness. While the electrolyte-leakage measurements gave an estimate of damage inflicted on the plasma membrane, plastocyanin release was measured to probe the intactness of the thylakoid membrane system after a freezethaw cycle. The frost hardiness of the thylakoids in situ increased by 4C over 24 h of salt stress to the seedlings. Over the first 5 h, hardening was six times faster in thylakoids than in the plasma membrane. This rapid increase in hardiness in vivo was reflected in reduced in-vitro freeze-thaw damage to thylakoids isolated from seedlings after only 1 h of salt stress.
Inorganic solutes are shown to alter the permeability of root and leaf tissues. Experiments with beet root tissues reveal that CaCl(2) decreases leakage of betacyanin from the tissue, that (NH(4))(2)SO(4) increases leakage, and that each salt can relieve the effects of the other. A comparison of cations and anions shows a range of effects with the various solutes. Experiments with Rumex obtusifolius L. leaf discs reveal that whereas CaCl(2) defers the development of senescence, (NH(4))(2)SO(4) hastens senescence and increases the leakage of materials out of the leaf discs. The solute effect on Rumex obtusifolius L. is prevented by gibberellin. CaCl(2) can relieve the (NH(4))(2)SO(4) effect. The results are interpreted as indicating that the inorganic solutes may serve to alter the permeability of membranes through alterations of interactions between water and macromolecules in the tissues; the interpretation is consistent with the evidence for opposite effects of Ca and NH(4), the effective concentrations being about 10(-3)m, and the reversibility of the effects of one solute by another of opposite stabilization-destabilization effect.