From Plant Biostimulants
Primarenc and the effects of temperature on flowering and fruit set in vegetables. The significant effect of temperature on flowering is well-documented. Studies in peppers have demonstrated the effects of night temperatures on the female and male organs of flowers. The results all showed that, when night temperatures go down from 20 °C to 12-10 °C, the ovary is large and the length of the style is reduced. Furthermore, the number of grains of viable pollen and their germinating power were significantly reduced when night temperatures were lower. Values went down from 3.5 x 105 grains of pollen with a 40 % germination rate at 20 °C, to less than 5000 grains of pollen with only a 5 % germination rate at 10 °C. The receptivity of the stigma and the capacity of the style to facilitate the growth of pollen tubes were also affected when night temperatures went down from 20 °C to 12-10 °C.
The abnormalities induced by high and low temperatures in tomato flowers were studied in the same way. The optimal conditions for fertilisation and fruit set to occur in tomato plants were 14-17 °C at night and 23-25 °C during the day. Thus, for example, a too high temperature (more than 30 °C) or a too low temperature (less than 10 °C), may result in the formation of sterile pollen and deformations in the anthers. Thermal limits for normal fructification to occur are a maximum of 30-32 °C and a minimum of 10-12 °C.
Fruit set, which is essential for a good yield, is affected by high temperatures at different stages. Ovule fertility, as well as pollen quantity and fertility, are reduced when flowers are exposed to 35 °C. In addition, pollen transfer is altered since flowers suffer from deformations that prevent it from reaching the stigma. Pollen germination and pollen tube growth are also very negatively affected when temperatures are above 35 °C.
The process through which plants receive the signals of stressful environmental factors and transmit them to the cellular machinery to activate adaptive and defence responses is called signal transduction. For signal transduction to occur, the action of a “signalling pathway or cascade” is required, that is to say, the transfer of stimuli from a primary receptor molecule (which receives the stimulus and is called receptor), through a combination of molecules (called signalling molecules), whose function is to transmit the signal by means of a chemical event to the molecules or genes that are in charge of the response to the stimulus (called effectors). This process is called cascade because it is a chain reaction –the action of the previous agent being required at each step– although it is not strictly linear. Indeed, a signalling molecule can activate one or more effectors or an effector may be activated by two or more signalling molecules.
One of the factors responsible for damage under adverse environmental conditions is the excessive production of active oxygen species, such as superoxide (O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (OH-). This oxidation stress occurs in plants exposed to low and high temperatures, and to other types of stress such as high irradiance, drought, UV radiation, exposure to atmospheric pollutants, herbicides, etc.
Reactive oxygen species and oxygen free radicals are able to damage lipids of the cellular, mitochondrial and chloroplastic membranes. Moreover, the DNA and proteins may undergo oxidative damage, which degrades them. This oxidative damage is the price aerobic organisms must pay to carry out their different metabolic activities in an unfavourable environment.
Nonetheless, throughout their evolution, plants have developed defences against this type of oxidative damage. These defence mechanisms, in the form of biochemical compounds and antioxidants, stabilise, prevent or repair the different biomolecules, thus ensuring maximum protection against oxidative damage.
Oxidative stress is defined as the specific biochemical state of a cell or tissue in which the generation of oxidative chemical species exceeds the plant’s capacity to produce antioxidants or the activity of these latter and that of free radical trapping in the cell.Oxidative stress reduction test with primarenc
This test aimed to evaluate the oxidative level as an indicator of thermal stress and peroxidation of lipids as an indicator of cell damage in the leaf tissue of a tomato plant subject to situations of stress due to low and high temperatures. The variation experienced by these levels after the application of primarenc as an anti thermal stress product was also determined.
Two temperature regimes were set in two growth chambers. These were applied 12 days after transplant and were maintained until the end of the test:
Day temperature: 10 °C
Night temperature: 4 °C
Day temperature: 40 °C
Night temperature: 28 °C
Both temperature regimes included 2 treatments:
T1: control group, no application
T2: one application of primarenc via irrigation at a dose of 0.12 g per plant 12 days after transplant.
84 tomato plants per chamber (cv. Boludo, from the Seminis company), in pots with coco fibre as a substrate, were used for the test. The parameter that was measured was the evolution of hydrogen peroxide levels in leaf tissues as an indication of thermal stress over a 7-day period. The determinations were carried out in 4 tomato plants per temperature regime, treatment and sampling time.Effect of low temperatures on hydrogen peroxide levels
Hydrogen peroxide [H2O2] concentration (nmol/gPF)Effect of high temperatures on hydrogen peroxide levels
Hydrogen peroxide [H2O2] concentration (nmol/gPF)Evaluation on the effect of primarenc as a thermal anti-stress and its repercussion in the fruit set of the crop habanero chili pepper
In the Yucatan Peninsula (Mexico), the production of vegetables and fruits are affected by extreme day and night temperatures, in both the spring – summer and autumn – winter production cycles.
In this study, the registered temperatures during the day where 39-43 °C and 6-9 °C at night, thus having repercussions in a high percentage of aborted flowers and little fruit set.
- Crop: Habanero chili pepper
- Place: Tizimin, Yucatán (México)
- Maximum temperature 40 ºC and minimum 12 ºC
- Precipitation 1200mm
- Population density: 20.830 plants per/ ha
- Primarenc doses : 2 gr / litre of water
- Applications at the beginning of flowering and 15 and 21 days after the first application.
- Crop: courgettes cv. Lioness F1
- Place: Tekax, Yucatán (México)
- Maximum temperature 35 ºC and minimum 8 ºC (October, November and December)
- Precipitation 1200mm
- Population density: 27.780 plants per/ ha
- Primarenc doses : 1.5 gr / litre of water
- First application 22 days after transplanting and 7 and 14 days after the first application.