Chilling and Freezing Temperature Stress Differently Influence Glucosinolates Content in Brassica oleracea var. acephala

Abstract

Brassica oleracea var. acephala is known to have a strong tolerance to low temperatures, but the protective mechanisms enabling this tolerance are unknown. Simultaneously, this species is rich in health-promoting compounds such as polyphenols, carotenoids, and glucosinolates. We hypothesize that these metabolites play an important role in the ability to adapt to low temperature stress. To test this hypothesis, we exposed plants to chilling (8 °C) and additional freezing (−8 °C) temperatures under controlled laboratory conditions and determined the levels of proline, chlorophylls, carotenoids, polyphenols, and glucosinolates. Compared with that of the control (21 °C), the chilling and freezing temperatures increased the contents of proline, phenolic acids, and flavonoids. Detailed analysis of individual glucosinolates showed that chilling increased the total amount of aliphatic glucosinolates, while freezing increased the total amount of indolic glucosinolates, including the most abundant indolic glucosinolate glucobrassicin. Our data suggest that glucosinolates are involved in protection against low temperature stress. Individual glucosinolate species are likely to be involved in different protective mechanisms because they show different accumulation trends at chilling and freezing temperatures.

Effects of Short-Term Exposure to Low Temperatures on Proline, Pigments, and Phytochemicals Level in Kale (Brassica oleracea var. acephala)

“…Under chilling temperature their content increased, while under additional freezing temperature their content decreased significantly. This trend is different from the one we reported previously, where the content of glucosinolates increases under chilling and freezing temperatures [12]. This different trend may be due to different experimental conditions and age of plants as reported in our previous work [12], where we exposed plants to freezing temperature for 1 h after 1 week of acclimation.…”

“…This trend is different from the one we reported previously, where the content of glucosinolates increases under chilling and freezing temperatures [12]. This different trend may be due to different experimental conditions and age of plants as reported in our previous work [12], where we exposed plants to freezing temperature for 1 h after 1 week of acclimation. Differences in glucosinolates trend reported in different papers are probably due to different experimental conditions, e.g., temperatures, duration of acclimation, etc., which may influence accumulation of different phytochemicals or be related to the kale variety.…”

“…The level of chlorophyll a, b, and total chlorophylls and carotenoids was decreased after exposure to chilling temperature, while staying stable under freezing temperature in similar concentration as in control plants. Freezing temperatures normally cause a decrease in the ratio of total chlorophyll to carotenoids [12], but the acclimatization period in chilling period was much longer, so decrease in chlorophylls can also be a response to long exposure to chilling rather than freezing itself.…”

“…Kale (B.oleracea var. acephala) is known for its good tolerance of environmental stress such as salt, drought and frost hardiness and resistance [8][9][10][11][12][13][14]. Kale is easy and cheap for cultivation and production significantly increased from 3994 to 6256 harvested acres in US, in the time from 2007 to 2012, respectively [15].…”

Low Temperatures Affect the Physiological Status and Phytochemical Content of Flat Leaf Kale (Brassica oleracea var. acephala) Sprouts

“…They are precursors of vitamin A, photoprocessors, antioxidants, immunity enhancers, and contribute to reproduction [44]. In this experiment, the total carotenoid content (Table 2) is comparable to values previously reported for kale sprouts [2], but the content in the sprouts is lower than the content of carotenoids in more mature kale plants [46,47] from the same variety. These results are in line with the report of Wojdyło et al [21] who compare carotenoid content in sprouts and microgreen and found several times more carotenoids in microgreens.…”