Huong Dong I. Khai nien • Huong dong cua thuc vat la mot hinh thuc phan ung cua mot bo phan cua cay doi voi cac tac nhan kich thich theo mot xu huong xac dinh. (huong dong o thuc vat xay ra tuong doi cham va duoc dieu tiet nho hoocmon thuc vat). • Huong dong o thuc vat gom co : huong dong duong va huong dong am. • Huong dong gom co cac kieu sau: II. Cac kieu huong dong 1.Huong dat ( huong trong luc). Phan ung sinh truong cua thuc vat dap ung lai voi tac dong cua trong luc (huong ve tam qua dat). Re huong dong duong, than canh huong dong am. Giai thich: Khi dat cay nam ngang, thi re cay moc quay xuong dat vi khi do auxin tap trung nhieu o phia duoi nen o re ham luon auxin qua cao nen lam kiem ham su tang truogn cua re. O than luong auxin tap trung nhieu nhung lam cho than sinh truogn nhanh keo dai than ra=> day re cay moc ve phia duoi. 2.Huong sang phan ung sinh truong cua thuc vat dap ung lai voi tac dong cua anh sang. Than canh huong dong duong, re huong dong am. Giai thich: Khi anh sang tac dong ve mot phia luong auxin tap trung nhieu o ben khong co anh sang chieu vao (vi auxn de bi phan huy boi anh sang). Nen ben chau nhieu auxin se sinh truong nhanh lam giup than dai ra day ngon c cay huong ve phia co anh sang. 3. Huong hoa phan ung sinh truong cua thuc vat dap ung lai tac dong cua hoa chat. Giai thich: Mot chau cay o giua co dat mot hop xop( co nhieu lo nh o thanh hop) dung phan bon( kali,dam) re cay sinh truong huong ve phia hop xop. Nguoc lai neu dat mot hop xop ma co chau chat doc(fluorua,arsenat) thi re cay se phat trine va huong xa hop xop. 4. Huong tiep xuc phan ung sinh truong cua thuc vat sap ung lai voi tac dong cua vat tiep xuc voi bo phan cau cay. Giai thich: Do toc do sinh truong khong dong due cua cac te bao o hai phia doi dien nhau. Luong auxin o phan khong tiep xuc voi coc leo nhieu nen lam cho phan than do sinh truong nhanh a dai ra con o phan than tiep xuc voi coc thi it auxin ne cham phat trien nen than thuc vat co hinh dang uon cong. 4. Huong nuoc phan ung sing truong cua thuc vat dap ung lai voi tac dong cau nuoc. Giai thich: Thuc vat moc o ven ao,ho thi bo re phat trine huogn ve phia co nguon nuoc. III. Vai tro cua huong dong trong doi song thuc vat Vai tro cua huong dong:huong dong giup cay sinh truong huong toi cac tac nhan moi truong thuan loi giup cho cay thich ung voi cac bien dong cu adieu kien moi truong de ton tai va phat trine tot. Chu y: hoocmon auxin de bi anh sang phan huy, tuy theo nguong nong do nhieu hay it hoocmon auxin co vai tro khac nhau. hoocmon auxin toi nguong nong do nhieu thi giup kha nang sinh truogn cua thuc vat nhanh hon, neu hoocmon auxin toi nguong nong do qua nhieu thi hoocmon auxin o luc nay la kiem ham kha nang sinh truong o thuc vat. . dinh. (huong dong o thuc vat xay ra tuong doi cham va duoc dieu tiet nho hoocmon thuc vat). • Huong dong o thuc vat gom co : huong dong duong va huong dong. am. • Huong dong gom co cac kieu sau: II. Cac kieu huong dong 1 .Huong dat ( huong trong luc). Phan ung sinh truong cua thuc vat dap ung lai voi tac dong