Boro no crescimento in vitro e na atividade enzimática do mirtileiro

Abstract

The blueberry is a small fruit rich in antioxidants which has increased its consumption in the last few years. The plantlets production can be made through micropropagation, resulting in plants with high phytosanitary quality. This technique uses as substrate different nutritional compositions in the culture medium, but with the same boron concentration. Under different concentrations of this nutrient it may occur enzymatic alterations, because of its essentiality in the plant’s metabolism. Thus, the purpose of this work was to study the effect of boron in the in vitro growth of the blueberry and in the enzymatic alterations. It was used the WPM supplemented with sucrose (20 g L-1), myo-inositol (0,01 g L-1) and agar (6,0 g L-1). For every experiment the design was completely randomized. In the first experiment of in vitro multiplication (evaluated at 90 days) the factorial scheme was 3x4, with 3 concentrations of 2-isopentalinadenine - 2iP (0,0, 2,5 and 5,0 mg L-1) and 4 concentrations of boric acid (0,0, 3,1, 6,2 and 9,3 mg L-1). Another two experiments were made to evaluate the effect of different concentrations of boron (0,0, 3,1, 6,2 and 9,3 mg L-1), one under the influence of 2iP (5,0 mg L-1) and another one under the high concentration of indolbutyric acid - IBA (2,5 mg L-1), both evaluated at 180 days and in a unifactorial scheme. For all the experiments it was used 4 repetitions composed by 5 explants. It was evaluated the length of the aerial part and of the largest root, the number of the shoots and leaves, fresh weight, rooting percentage and the activity of the enzymes polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), peroxidase (POD) and indoleacetic acid oxidase (IAAO). In the first experiment it was noticed that the 6,2 mg L-1 of boron generated the biggest shoot formation (18,4), as well as 5,0 mg L-1 of 2iP (25,5). In the interaction between these concentrations of boron and 2iP, there was the biggest activity of the POD and PPO enzymes, which are responsible for the synthesis of compounds such as lignin. On the second experiment, in the conditions of boron deficit, it was observed bigger quantity of shoot-tip necrosis (9), red leaves (31) and high activity of the PAL, IAAO and POD enzymes. The roots growth and the rooting were inhibited, showing how essential boron is in this phase of development. In an auxin-free medium the IAAO had a negative correlation with the root’s growth, meanwhile in the medium with IBA the correlation with the rooting was positive. Therefore, it was concluded that the boron concentration of 6,2 mg L-1 and the 2iP concentration of 5,0 mg L-1 had better results for the multiplication of the blueberry, in deficiency conditions occurs the increase of enzymatic activity and the blueberry rooting depends of the boron and the IAAO.