*5.1.1 Chilling injury*

The physiological damage induced by temperatures between 0 and 12°C is known as chilling injury [43]. Chilling is a problem for many thermophilic plants. The temperature and length of exposure determine the severity of the injury. Injury is usually not obvious during chilling, but appears once the temperature rises. Chilling injury causes wilting and browning of the leaves; severe chilling causes plants or plant sections to die. The chilling injury could be caused primarily by membrane dysfunction at low temperatures.

## *5.1.2 Chilling before emergence*

Long-term cold temperatures destroy the Imbibed seeds that have been killed. Researcher also looked explored the effects of a 28-day cold treatment on six different types of plants. Varietal survival differences were observed. At 4 and 6°C, the average mortality was 36 and 21%, respectively; there was hardly little harm at 8 and 10°C. Sugars, and amino acids were exuded from maize seeds when incubated at a low temperature. This exudation was substantially higher at 6 than at lWC, and it could be linked to membrane malfunction at the lower temperature. They identified a specific chilling injury after imbibition in very dry seeds incubated at 5°C. During initial hydration, structural defects in the radicle caused the injured [44].

Young plants were injured by a 6-day exposure to 1°C and an 8-day exposure to 2.5°C. Chilling generated ultrastructural alterations in the meristematic cells of primary roots. The Golgi apparatus and inner mitochondria1 membranes were destroyed after 3 days of cooling, Lipid bodies had accumulated, and the endoplasmic reticulum had decreased. After 4 days of cooling, researchers discovered double cells made up of a small cell inside a larger cell. According to the findings, temperatures below roughly 6°C damage or kill immature maize plants. Temperature, length of cold treatment, developmental stage, and genotype all influence the severity of the injury [44].

In the field, there is no data on how cold affects germination. It is doubtful that chilling will have an impact on Maize's survival and emergence because the crop is sown late in the spring when soil temperatures rarely fall below 6°C for long periods.

## *5.1.3 Chilling after emergence*

Using 7-day-old maize seedlings, Miedema [44] investigated chilling effects at 0.3°C and low light intensity. The seedlings were moved to a temperature of 21°C to explore the physiological and biochemical consequences. Leaf damage began to appear after 36 h of exposure to the cold, and by 72 h, the damage had become irreversible. Leaf extension at 21°C was drastically reduced after 24 and 36 h of chilling. Increasing ion leakage and oxygen uptake in chilled plant leaf segments due to uncoupling oxidative phosphorylation. Plants that were chilled for 72 h did not occur this.

According to the findings of several researchers, seedlings that had been chilled in an air-conditioned greenhouse at 2–4°C for 60 h developed transverse chlorotic

bands the leaf blades 5–10 days after the chilling period. As a result of the chilling process, bands of color began to emerge on the blades used to generate the plant's curled appearance. The researchers discovered similar necrotic cross bands and other leaf damage in maize seedlings that had been exposed to 4°C in the dark for three days [44]. After transfer normal temperatures, the majority of the damage disappeared. After 6 days of exposure to 4°C, irreversible leaf damage occurred.

After 14 days of exposure to a daylight temperature of 10/4°C, chlorotic cross bands were developed, but not at 16/4°C. Chilling sensitivity was higher in the cell extension zone of the leaves than in full-grown or meristematic tissue. The tissue between the veins was chlorotic in some cross bands, whereas tissue along the veins (bundle sheath) was green. Various thermophilic Gramineae have chlorotic cross bands. Its found that transverse permanently chlorotic bands appeared in *Sorghum bicolor*, *Paspalum dilatatum*, and Digitaria smut-sii following a single cold night. Chlorophyll-deficient chloroplasts with disorderly lamellae were detected in most mesophyll cells in the chlorotic bands, whereas chloroplasts in bundle sheath cells were green and had a normal structure. The nucleus and mitochondria of chlorotic mesophyll cells showed no structural changes.

Because of the chilling sensitivity of the chloroplasts, leaves appear to be more sensitive to chilling than other organs. Chilling treatments cause visible injury to the roots of maize seedlings. In the case of Maize, there was just a minor amount of genetic heterogeneity in chilling-induced leaf damage [44]. Chlorotic cross bands are frequently seen after a cold spell in the field. They could result from a combination of low temperature and high light intensities, or they could be the effect of chilling during cold nights.

### *5.1.4 Chilling injury at high light levels*

When maize leaves are exposed to a temperature of 10°C and a light intensity of 170 W m-\*, they develop necrotic lesions, according to Taylor and Rowley [45]. With increasing exposure time to very low levels on the third day, the photosynthetic rate at 10°C steadily decreased. A permanent photosynthetic capacity reduction was caused by this chilling treatment; Photosynthesis at 25°C was reduced by 40% and 70% after 1.5 and 2.5 days of cooling. The chilling treatment did not affect chlorophyll levels. According to Taylor and Craig [46] in Sorghum, this form of injury was related to edoema and changes in the ultrastructure of chloroplasts. The membranes of the thylakoids first closed together as the starch grains vanished, but with more severe stress, the thylakoids moved apart, and granal stacking vanished. Paspalurn and soybean both had similar effects.

When maize plants were subjected to the light intensity of 13°C and 350 W mP2, a decrease in photosynthetic rate was seen, similar to what Taylor and Rowley [46] discovered. They found that throughout a 10-day exposure period, photosynthesis of maize seedlings cultured at 10°C and 105 Wm−2 fell only 30%. The photosynthetic rate immediately restored to its previous level when the seedlings were reintroduced to 22°C. Temperatures of around 10°C in combination with strong light levels, in general, cause the forms of damage already mentioned. When Taylor and Rowley [46] employed conditions similar to those experienced in the field at the start of the growing season, they discovered that seedling growth was impeded.

### **5.2 Male sterility induced by low-temperature**

Plants grown in a greenhouse with short photoperiods and cool nights (10°C) showed male sterility throughout flowering. The tassel growth stage was used to gauge the degree of sterility achieved during the cold treatment. Low night

temperatures have also been linked to male sterility in rice and Sorghum [47], but not in Maize under field circumstances.
