With the vines tightly binding your arms and legs, you can't even try to get away. They start taking advantage of that by tearing away your clothes quickly, leaving you totally naked. A vine reaches for your crotch and wraps around your rapidly hardening penis and starts rubbing it, even faster than your hand usually can. You pant, and realize as you look down that a strange translucent liquid is being seeped into your skin from the vines. For a moment you're worried, but it quickly starts to sedate you, making you feel pleasant.
Another, thicker vine slides around your midriff and tightly grips you, forcing your figure to change. You grunt, but the touch of the vines and the feelings from the liquid now in your bloodstream dull any pain, and your skin feels softer and smoother once it lets you go. Your hips flare and your butt fills out as it does, and you start to realize: the vines are turning you into a woman.
Two more of them move to your chest and start running over and cupping your nipples, quickening the changes further. You feel your nipples perk up and start to become larger and puffier, accumulating flesh around them as your body starts forming breasts. Your moans become more frequent and higher-pitched as the warm vines continue rubbing your skin, softening it all over.
The vines finally start to change the last male part of you. The vine that's been stroking your penis this whole time tightens its grip, and another one moves to touch your crotch directly. Almost as soon as it touches the line in the middle of your scrotum, the testicles pull up inside you and the loose skin starts to separate and form labial lips, a slit leading inside your body forming between them. The tight rubbing around your penis causes it to shrink rapidly until it settles atop your pussy as a tiny sensitive nub.
You look at your body in amazement. The vines turned you into a woman!